Genetics Quick Review of Grade 11 Sex Linked Traits Sex Influenced Traits Polygenic Traits Epistatic Genes.

GeneticsQuick Review of Grade 11

Sex Linked Traits

Sex Influenced Traits

Polygenic Traits

Epistatic Genes

How many chromosomes do humans have?

• 46…or 23 homologous pairs

• 23 from your mother and 23 from your father

•Which chromosomes determine if you’re a girl or boy?

• Pairs1 through 22 = autosomal chromosomes

Two Types of Cells1. Somatic Cells – All body cells,

diploid (2n)

2. Sex Cells – Gametes, haploid (n)

Two Types of Chromosomes

1. Autosomal – All body cells

2. Sex Chromosomes – X and Y

The Sex chromosomes

If you get a Xyou’re a girl

Its all up toDad….

The Sex chromosomes

But... If you get a Y you’re a boy

Punnett Squares

X XX

Y

XX XX

XY XY

The set of genes that an organism

possesses

Expressed trait (physical appearance)

When two alleles are identical

Ex. DDWhen the two alleles are different

Ex. Dd

Different forms of the same

gene

Allele which controls the characteristic whenever it is present.

Allele whose characteristics only show up when it is present on both chromosomes

BB or Bb

bb

GeneticsQuick Review of Grade 11

Sex Linked Traits

Sex Influenced Traits

Polygenic Traits

Epistatic Genes

Sex Linked Traits

• Sex-linked traits are traits that are controlled by genes on the sex chromosomes

• Examples: –Colour Blindness–Hemophilia

3 Different Forms of Sex Linked Inheritance

1. X-linked recessive inheritance

2. X-linked dominant inheritance

3. Y-linked inheritance

Sex Linked Inheritance Notation

• X-linked recessive alleles are represented by a X with a superscript of either:

+ (dominant)

or

– (recessive)

Genotypes of Sex Linked Inheritance

• What are the possible genotypes of a sex linked inheritance for a female?

X+X+ X+X - X -X -

• What are the possible genotypes for sex linked inheritance for a male?

X+Y X - Y

1. X-linked Recessive Inheritance

X-linked recessive traits are traits resulting from a recessive allele on the X chromosome

Why do X-linked recessive traits show up more often in men than women?

Are YOU Colorblind?

Normal Color Vision:A: 29, B: 45, C: --, D: 26

Red-Green Color-Blind:A: 70, B: --, C: 5, D: -- 3.

Red Color-blind:A: 70, B: --, C: 5, D: 6 4.

Green Color-Blind:

A: 70, B: --, C: 5, D: 2

X-linked Recessive Inheritance

• Example #1: Colorblindness

• The allele that controls colorblindness is found on the X chromosome and is recessive

• What genotype must a female have to be diagnosed as colorblind?

X -X-

Possible Colorblindness Phenotypes

X+X+

Female with Normal Vision

X+X –

Female with Normal Vision (Carrier)

X -X –

Colour Blind Female

X+Y –

Male with Normal Vision

X – Y

Colour Blind Male

Let’s try a cross: X+X– • X+Y

• Phenotypes– Females:– Males:

Let’s try a cross: X+X– • X-Y

• Phenotypes– Females:– Males:

Let’s try a cross: X+X+ • X-Y

• Phenotypes– Females:– Males:

Let’s try a cross: X-X- • X+Y

• Phenotypes– Females:– Males:

Try these questions on your own:

1. A woman who is heterozygous (a carrier) for colorblindness marries a man with normal vision. What will be the possible phenotype ratio of their children?

2. What is the probability that the sons of a homozygous recessive mother would be colour blind?

*Remember to represent colorblindness with a “-”

More examples of X-linked Recessive Inheritance

• Example #2: Hemophilia

• Hemophilia is a serious ailment in which the blood lacks a clotting factor, and therefore when an individual is injured, they cannot stop bleeding

• About 1 in 4,000 males are born with disorder, much lower incidence in females

Hemophilia Pedigree

Just to make sure you got it! ;)

A woman who is heterozygous for hemophilia marries a normal man:

a. What are the genotypes of the parents?

b. Make a Punnett square for the cross

c. What is the probability that a male offspring will have hemophilia?

d. What is the probability of having a hemophiliac female offspring?

2. X-linked Dominant Inheritance

• X-linked dominant traits are traits that result from the presence of a dominant allele on the X chromosome

• Unlike X-linked recessive traits, females and males both require only ONE dominant allele in order to express the trait

X-linked Dominant Inheritance

• Example #1: Faulty Tooth Enamel and Dental Discoloration

• Individuals who have an X chromosome that carries a dominant allele for this trait will have dental discoloration.

Possible Dental Disorder Phenotypes

X+X+

Female with Dental Discoloration

X+X –

Female with Dental Discoloration

X -X –

Normal Female

X+Y

Male with Dental Discoloration

X – Y

Normal Male

Let’s think about it...

1. Would a heterozygous woman for dental discoloration display the trait?– Yes, because dental discoloration is a

X-linked dominant trait, so only one dominant allele is needed to express the trait

2. What percentage of the children from a heterozygous mother and an affected father would have dental discoloration?

3. Y-linked Inheritance

• Y-linked traits are controlled by alleles on the Y chromosome

• Another word for Y-linked traits is holandric traits (“wholly male”)

• Are females affected by Y-linked traits?

• Do the words homozygous or heterozygous apply to Y-linked traits?

What do these 2 have in common?

• Example of Y-Linked Inheritance – HAIRY EARS!

• Anthony Victor (India) has hair sprouting from the centre of his outer ears (middle of the pinna) that measures 18.1 cm (7.12 in) at its longest point.

All of the sons of an affected male will display this Y-linked trait

Last Sex-linked Trait Example

Eye color in fruit flies (Drosophilia melanogaster )

• Eye color is controlled by the X chromosome

• Red eyes are dominant to white

• White eyes are most common in males

• Females only display white eyes if they are homozygous recessive for the trait

Fruit Flies Continued

• What type of X-linked inheritance is this?

• Try your new knowledge out on the handout you are about to receive!

X-linked recessive Inheritance because the males show the trait more often that the females. Also, the females must have two X chromosomes, both of which carry the recessive alleles for white eye color in order to have white eyes!

GeneticsQuick Review of Grade 11

Sex Linked Traits

Sex Influenced Traits

Polygenic Traits

Epistatic Genes

What’s the Difference?

• Sex-Linked Traits: alleles on sex

chromosomes

• Sex-Influenced Traits: alleles on autosomal

(1-22) chromosomes

Sex-Influenced Traits

• Controlled by a pair of alleles on autosomal chromosomes but its phenotypic expression is influenced by the presence of certain hormones

• Can be seen in BOTH sexes, but will vary in frequency between the sexes or in the degree of the phenotypic expression

Estrogen, Progesterone, Testosterone, etc.

Sex-Influenced Traits

• Example #1: Pattern Baldness

• Pattern Baldness can occur in both males and females, but is much more common in males….

Why?

– Because the pattern baldness trait is influenced by the hormone testosterone

Unlike male-pattern baldness, female-pattern baldness is an over-all

thinning which maintains the normal hairline

The combination of alleles for pattern baldness will lead to different phenotypic expressions

depending on the sex of the individual

Possible Pattern Baldness Phenotypes

Example: Let B represent the non-bald allele

BB

Non-bald in both sexes

bb

Bald in both sexes

Bb

Bald in men

Non-bald in females

The “B” allele acts as a dominant allele in the

heterozygous genotype in females, but acts as a recessive allele in the

heterozygous genotype of the male

Let’s check your understanding…

• What would Locke’s genotype be?

Bb or bb

• What about his ‘we’ll-assume-for-the-sake-of-this-example’ balding mother?

bb

To solve these questions, we can use simple Monohybrid Crosses

Then able to make conclusions regarding phenotypes based on the

sex of the individual

Now you try…

A heterozygous balding male reproduces with a heterozygous normal female.

– Do the cross and determine the phenotypic ratios for males and females

Let’s make it personal…

What is the probability that YOU will be bald if your father is homozygous and

balding, and your mother is homozygous and not balding?

If only it were that simple!

• Hair is controlled by many different factors including several alleles and environmental factors (polygenic traits)

• So, we cannot fully explain pattern baldness using sex-influenced inheritance.

• It is not easy to explain the diversity found in different ages of onset, as well as severity of baldness.

More Sex-Influenced Trait Examples

A male homozygous for clubfoot reproduces with a normal homozygous female.

What are the genotypes and phenotypes of their children if testosterone alters the phenotypic expression of the trait in the heterozygous expression?

Let F represent normal feet

Let f represent clubfoot.

More Sex-Influenced Trait Examples

Two heterozygous individuals get married and have lots of children. The father suffers with a painful condition called gout.

What are the parent’s genotypes?

What are the genotypes and phenotypes of the children?

Let G represent no gout

Let g represent gout

More Sex-Influenced Trait Examples

Rheumatoid arthritis occurs more often in females than males due to the presence of estrogen. A heterozygous woman marries a heterozygous male

RR would cause the condition in both sexes. A homozygous recessive, rr, genotype would prevent the disorder in both sexes

More Sex-Influenced Trait Examples

Singing voice!

The genotype that causes males to have a high tenor voice causes females to have a deep contralto voice. The genotype that causes males to have deep bass voices is the same genotype that causes females to have high soprano voices!

Design a question involving the Sex-

Influenced trait of singing voice

GeneticsQuick Review of Grade 11

Sex Linked Traits

Sex Influenced Traits

Polygenic Traits

Epistatic Genes

Polygenic Traits

• Those traits that are determined by the combined effect of 2 or more pairs of alleles

• Each pair of alleles adds something to the resulting phenotype

• Other names for polygenic traits are: multi-factorial traits or quantitative traits

Polygenic Traits

• Because so many alleles contribute to the final phenotype, a variety of phenotypes can occur!

• For example, height is a polygenic trait

To solve polygenetic trait questions that are only controlled by 2 pairs of alleles,

we can use a Dihybrid Cross (Punnett Square)

Polygenic Traits

• Example #1: Pepper Colour

Gene 1: R = red r = yellow

Gene 2: Y = absence of chlorophyll (no green) y = presence of chlorophyll (green)

Possible Pepper Colour Phenotypes

R -Y –

Red (Red/No Chlorophyll)

R – yy

Brown/Orange (Red/Chlorophyll)

rrY –

Yellow (Yellow/No Chlorophyll)

rr/yy

Green (Yellow/Chlorophyll)

Pepper Colour Questions

• Try crossing a brown pepper (RRyy) with a yellow pepper (rrYY).

• Which trait will your offspring (F1 generation) produce?

• What traits are produced when you cross two of the peppers found in the F1 generation?

Polygenic Traits

• Example #2: Chicken Combs

Comb shape is controlled

by 2 genes found on 2

different pairs of

chromosomes

Gene 1: R

Gene 2: P

Possible Chicken Comb Phenotypes

R – pp

Rose Combs

R -P –

Walnut Combs

rrP –

Pea Combs

rr/pp

Single Combs

Practice Makes Perfect!

Indicate the phenotypes of the parents and give the genotypic and phenotypic ratios of their offspring for the following crosses:

1. rrPP x RRpp

2. RrPp x RrPp

**Refer to your phenotype chart for chickens

Polygenic Traits

• Example #3: Hair Colour

Hair colour is controlled by

alleles on chromosomes 3,

6, 10 & 18

The most dominant alleles

that appear in the genotype,

the darker the hair

Polygenics Plant Height Problem

The height of plants is controlled by 4 pairs of alleles. Alleles A, B, and C contribute 3 cm to the plant's height.

Alleles that are recessive do not contribute to the height. Gene L is always found in a homozygous dominant condition and always contributes 40 cm to the height.

1. What would be the height of a plant with the genotype AABBCCLL?

2. What would be the height of a plant with a genotype aabbccLL?

3. What would be the height of the offspring produced from a cross between the plants in a) and b)?

4. What would be the heights of the offspring produced from a cross between AaBbCcLL and AaBbCcLL? (now there is a challenge!)

GeneticsQuick Review of Grade 11

Sex Linked Traits

Sex Influenced Traits

Polygenic Traits

Epistatic Genes

Epistasis

• Epistasis is a form of a gene interaction in which one pair of alleles (gene) masks the phenotypic expression of another

• There are no new phenotypes produced by this interaction

Epistatic versus Hypostatic

• Epistatic: the alleles that mask the effect

• Hypostatic: the alleles whose effect is being masked

Epistatic trait questions can be solved like polygenic trait questions with a

Dihybrid Cross

The difference is that there is now one pair of alleles masking the other