GENETICS Chapters 11 and 14
Feb 24, 2016
GENETICSChapters 11 and 14
GENETICS The scientific study of heredity- how
traits are passed down to offspring
TRAIT---Specific characteristic ( blonde hair, blue eyes)
GENE A hereditary unit consisting of a
sequence of DNA that occupies a specific location (LOCUS) on a chromosome and determines a particular characteristic in an organism.
(Genes undergo mutation when their DNA sequence changes)
LOCUS (LOCI PLURAL) Is a location on a
chromosome where a gene occurs
Loci will be written as-----6p21.2
6- chromosome number
P- arm 21.2- distance from
centromere
CHROMOSOME MAP / IDIOGRAM
Detailed diagram of all the genes on a chromosome
CHROMOSOME NUMBER DIPLOID- cell that contains all the
chromosomes of an organism (Humans= 46)
HAPLOID- cell that contains only HALF the chromosomes of an organism (ex- egg or sperm cell) (Humans=23)
CHROMOSOMESSEX CHROMOSOMES- chromosomes that
are responsible for determining sex of an organism (ex- X and Y in humans)
AUTOSOMES- chromosomes that determine traits other than sex in an organism (ex- humans- chromosome 1-22)
HOMOLOGOUS (PAIR) CHROMOSOMES pair of chromosomes that carry the same
genes
You will have one from each parent, they will both code for the same types of characteristics
KARYOTYPE a photograph that shows the complete
DIPLOID set of chromosomes arranged in homologous pairs and arranged in order of decreasing size.
ALLELE Alternate forms of a gene/factor. Examples:
--brown eyes vs blue eyes --blonde hair vs brown hair
--dimples vs no dimples
FATHER OF GENETICS
Gregor Mendel
GREGOR MENDEL An Austrian Monk (1822-1884) Developed these principles without
ANY scientific equipment - only his mind.
Tested over 29,000 pea plants by crossing various strains and observing the characteristics of their offspring.
GREGOR MENDEL Studied the following
characteristics:1. Pea color (Green,
yellow)
2. Pea shape (round, wrinkled)
3. Flower color (purple, white)
4. Pod shape ( inflated,
constricted)
5. Pod color (green, yellow)
6. Plant height (tall, short)
7. Flower position(axial, terminal)
MENDEL’S EXPERIMENTSMendel noticed that some plants always produced offspring that had a form of a trait exactly like the parent plant. He called these plants “purebred” plants. For instance, purebred short plants always produced short offspring and purebred tall plants always produced tall offspring.
Mendel called these the P 1 generation. (pure bred, parental)
X
Purebred Short Parents
Purebred Tall Parents
X
Short Offspring
Tall Offspring
MENDEL’S FIRST EXPERIMENT
Mendel crossed purebred plants with opposite forms of a trait. He called these plants the parental generation , or P generation. For instance, purebred tall plants were crossed with purebred short plants.
Parent TallP generation
Parent ShortP generation
X
Offspring TallF1 generation
Mendel observed that all of the offspring grew to be tall plants. None resembled the short short parent. He called this generation of offspring the first filial , or F1 generation, (The word filial means “son” in Latin.)
MENDEL’S SECOND EXPERIMENT
Mendel then crossed two of the offspring tall plants produced from his first experiment.
TallF1 generation
X
3⁄4 Tall & 1⁄4 ShortF2 generation
Mendel called this second generation of plants the second filial, F2, generation. To his surprise, Mendel observed that this generation had a mix of tall and short plants. This occurred even though none of the F1 parents were short.
Parent Plants Offspring
TERMS TO KNOW
MONOHYBRID CROSS- cross using only one trait
SELF CROSS- (SELF FERTILIZATION)- produce offspring asexually
P1 GENERATION-- parents- usually pure bred
F1 GENERATION- 1st set of offspring (1st family)
F 2 GENERATION- 2nd set of offspring (2nd family)
TYPES OF ALLELES Dominant: An allele which is expressed
(masks the other). Recessive: An allele which is present
but remains unexpressed (masked)
PHENOTYPE VS GENOTYPE Genotype: combination of alleles an
organism has. (Ex- BB, Bb, or bb )
Phenotype: How an organism appears.(Ex- brown hair, blonde hair )
GENOTYPES Homozygous: Both alleles for a trait
are the same. (BB- homozygous dominant, bb homozygous recessive)
Heterozygous: The organism's alleles for a trait are different. (Carrier of the recessive allele) Bb
DEVELOPED 3 LAWSLAW OF DOMINANCE- one allele always
shows of the other
LAW OF INDEPENDENT ASSORTMENT- states that each pair of genes (chromosomes) separate independently of each other in the production of sex cells. (example– you could have brown hair and blue eyes)
LAW OF SEGREGATION-
MENDEL’S LAW OF SEGREGATION
Mendel’s first law, the Law of Segregation, has three parts. From his experiments, Mendel concluded that:
1. Plant traits are handed down through “hereditary factors” in the sperm and egg.
2. Because offspring obtain hereditary factors from both parents, each plant must contain two factors for every trait.
3. The factors in a pair segregate (separate) during the formation of sex cells, and each sperm or egg receives only one member of the pair.
PREDICTING OFFSPRING Punnett square
INCOMPLETE DOMINANCE A third (new) phenotype appears in the
heterozygous condition. Flower Color in 4 O’clocks
RR = red rr = white Rr = pink
PROBLEM: INCOMPLETE DOMINANCE
Show the cross between a Red and a White flower.
-RR (0), Rr (4); rr (0)
- pink (4); white ()
R R
r
r
GENOTYPES:
PHENOTYPES:
PROBLEM: INCOMPLETE DOMINANCE
Show the cross between a Pink and a Pink flower.
- RR (1); Rr (2), rr (1)
-Red (1) pink (2); white (1)
R
r
GENOTYPES:
PHENOTYPES:
R r
CODOMINANCE The heterozygous condition, in which both
alleles are expressed equally Sickle Cell Anemia in Humans
NN = normal cells
SS = sickle cells NS = some of each
PROBLEM: CODOMINANCE Show the cross between an individual with
sickle-cell anemia and another who is a carrier but not sick.
N S
S
S
NS
NS
SS
SS
- NS (2) SS (2)- ratio 1:1
- carrier (2); sick (2)- ratio 1:1
GENOTYPES:
PHENOTYPES:
MULTIPLE ALLELES
There are more than two alleles for a trait
Blood type in humans Blood Types?
Type A, Type B, Type AB, Type O Blood Alleles?
A, B, O (in book – IA, IB, I)
PROBLEM: MULTIPLE ALLELES
Show the cross between a mother who has type O blood and a father who has type AB blood.
- AO (2) BO (2)- ratio 1:1
- type A (2); type B (2)- ratio 1:1
GENOTYPES:
PHENOTYPES:
O O
A
B
AO
BO
AO
BO
PROBLEM: MULTIPLE ALLELES
Show the cross between a mother who is heterozygous for type B blood and a father who is heterozygous for type A blood.
-AB (1); BO (1); AO (1); OO (1)- ratio 1:1:1:1
-type AB (1); type B (1) type A (1); type O (1)- ratio 1:1:1:1
GENOTYPES:
PHENOTYPES:
A O
B
O
AB
OO
BO
AO
Dihybrid Cross:a cross that shows the possible
offspring for two traitsFur Color:
B: Black b: White
Coat Texture:R: Roughr:
SmoothIn this example, we will cross a heterozygous individual with
another heterozygous individual. Their genotypes will be:
BbRr x BbRr
DIHYBRID CROSSBbRr x BbRr
First, you must find ALL possible gametes that can be made from each parent.
Remember, each gamete must have one B and one R.
DIHYBRID CROSSBbRr x BbRr
Possible gametes:BRBrbRbr
Next, arrange all possible gametes for one parent along the top of your Punnett Square, and all possible gametes for the other parent down the side of your Punnett Square…
DIHYBRID CROSS
Fur Color:B: Black b: White
Coat Texture:R: Roughr:
Smooth
BbRr x BbRr B
RbR
br
bR
Br
BR
br
Br
Then, find the possible genotypes of the offspring
DIHYBRID CROSS
Fur Color:B: Black b: White
Coat Texture:R: Roughr:
Smooth
BbRr x BbRr
BR
bR
br
bR
Br
BR
br
BrBBRR
BbRR BbRr
BBRr BBrr BbRr Bbrr
BbRR BbRr bbRR bbRr
BbRr Bbrr bbRr bbrr
BBRr
BR bR
br
bR
Br
BR
br
Br
BBRR
BbRR
BbRr
BBRr BBrr BbRr Bbrr
BbRR
BbRr bbRR
bbRr
BbRr Bbrr bbRr bbrr
BBRr
How many of the offspring would have a black, rough coat?How many of the offspring would have a black, smooth coat?How many of the offspring would have a white, rough coat?How many of the offspring would have a white, smooth coat?
Fur Color:B: Black b: White
Coat Texture:R: Roughr:
Smooth
BR bR
br
bR
Br
BR
br
Br
BBRR
BbRR
BbRr
BBRr BBrr BbRr Bbrr
BbRR
BbRr bbRR
bbRr
BbRr Bbrr bbRr bbrr
BBRr
How many of the offspring would have black, rough coat?How many of the offspring would have a black, smooth coat?How many of the offspring would have a white, rough coat?How many of the offspring would have a white, smooth coat?
Fur Color:B: Black b: White
Coat Texture:R: Roughr:
Smooth
Phenotypic Ratio
9:3:3:1
CHAPTER 12--SEX LINKAGE All chromosomes are homologous
except on sex chromosomes. Sex chromosomes are either X or Y. If an organism is XX, it is a female, if
XY it is male. If a recessive allele exists on the X
chromosome. It will not have a corresponding allele on the Y chromosome, and will therefore always be expressed
is an important tool for studying inherited diseases
uses family trees and information about affected individuals to:figure out the genetic basis of a
disease or trait from its inheritance pattern
predict the risk of disease in future offspring in a family (genetic counseling)
PEDIGREE ANALYSIS
How to read pedigreesBasic patterns of inheritance
1. autosomal, recessive2. autosomal, dominant3. X-linked, recessive4. X-linked, dominant (very rare)
HOW TO READ A PEDIGREE
Sample pedigree - cystic fibrosis
femalemale
affected individuals
Autosomal dominant pedigrees
1. The child of an affected parent has a 50% chance of inheriting the parent's mutated allele and thus being affected with the disorder.
2. A mutation can be transmitted by either the mother or the father.
3. All children, regardless of gender, have an equal chance of inheriting the mutation.
4. Trait does not skip generations
Autosomal dominant traitsThere are few
autosomal dominant human diseases (why?), but some rare traits have this inheritance pattern
ex. achondroplasia (a sketelal disorder causing dwarfism)
AUTOSOMAL RECESSIVE
1. An individual will be a "carrier" if they posses one mutated allele and one normal gene copy. 2. All children of an affected individual will be carriers of the disorder. 3. A mutation can be transmitted by either the mother or the father. 4. All children, regardless of gender, have an equal chance of inheriting mutations. 5. Tends to skip generations
Autosomal recessive diseases in humansMost common ones
• Cystic fibrosis • Sickle cell anemia• Phenylketonuria (PKU)• Tay-Sachs disease
AUTOSOMAL RECESSIVE