GENETICS

GENETICS

Gregor Mendel• “FATHER OF GENETICS” • Genetics-

scientific study of heredity; how traits are inherited

• Heredity the passing of traits

from parents to offspring

Mendel’s Pea Plant ExperimentsWhy Peas?

• Pea plants have many traits (tall/short, purple flowers/white flowers)

• self-fertilized or cross-fertilized

True-Breeding Plants:create plants that look like

themselves

Hybrid Plants: offspring of true-breeding plants

Tall x Short = Hybrid

Drill: April 2, 2012

• What is a gene? An allele?

• Define and differentiate between a true/pure-breed and a cross-breed/hybrid?

• Self-pollination vs cross-pollination: Explain each and how did Mendel prevent self-pollination.

Dominance-One trait dominates & “hides” the other

Tall x Short = all tall offspring (hybrids)

*Tall is the dominant trait* Short is recessive

Genes and AllelesMendel discovered that each trait is controlled by two factors

Genes – factors that determine your traitsAlleles-different forms of a gene

Mendel’s Experiments

Draw the crosses

Explaining the CrossWhen a parent makes sperm or eggs, their genes separate        (PRINCIPLE OF SEGREGATION)

Gametes contain either a T allele (tall) or a t allele (short)

Let's review what you know about genetics......

GENOTYPE  -  what genes the organism has (TT, Tt, tt)

PHENOTYPE   - what the organism looks like (tall or short)

Check for understanding

1.  A one-eyed purple people eater is crossed with a two eyed purple people eater.  All of their offspring have two eyes.   Which trait is dominant?

2.  If you use the letter E for this gene.   What is the genotype of the offspring?      Are these offspring the F1 or F2 generation?

4.  If you crossed the offspring with each other?  How many of the new offspring would you expect to have two eyes?

More checking

5.   The passing of traits from parents to offspring is known as  _________________

6.  Who was the father of genetics?  _________

7.  A single gene will code for a ______________, such as flower color.

8.  Every gene is made of two ______________

Drill: Thursday 5, 2011

1) How did Mendel find out whether the recessive alleles were still present in the F1 plants?

2) About one fourth of the F2 plants from Mendel’s F1 crosses showed the trait controlled ______ by the allele.

3) The dominant allele is represented by and a recessive allele is represented by

.

Probability: the likelihood that a particular event will occur

is called_______.

The probability that a single coin flip will come up heads.

• a. 100 percent • b. 75 percent• c. 50 percent • d. 25 percent

ProbabilityTRUE or FALSEThe past outcomes of coin flips greatly affect the

outcomes of future coin flips

Q: Why can the principles of probability be used to predict the outcomes of genetic crosses?

A: The way in which the alleles segregate is completely random, like a coin flip

Punnett Square can be used to predict and compare the genetic variations that will result from a

cross.

Show possible genotypes for the F2 offspring.

Practice #1:

In seals, the gene for the length of the whiskers has two alleles. The dominant allele (W) codes long whiskers & the recessive allele (w) codes for short whiskers.

a) What percentage of offspring would be expected to have short whiskers from the cross of two long-whiskered seals, one that is homozygous dominant and one that is heterozygous?

b) If one parent seal is pure long-whiskered and the other is short-whiskered, what percent of offspring would have short whiskers?

Practice #2:

A green-leafed luboplant (I made this plant up) is crossed with a luboplant with yellow-striped leaves. The cross produces 185 green-leafed luboplants.

Summarize the genotypes & phenotypes of the offspring that would be produced by crossing two of the green-leafed luboplants obtained from the initial parent plants.

Allele TypesDefinitions• Organisms that have two identical alleles• particular trait (TT or tt) Homozygous• Organisms that have two different alleles• same trait (Tt) Heterozygous• Physical characteristic of an organism Phenotype• Genetic makeup of an organism (Tt) Genotype

Independent Assortment• In a 2-factor cross, Mendel followed 2 genes

passed from one generation to the next

• Phenotype Genotype (true-bred)

a. round yellow peas __RRYY_b. wrinkled green peas __rryy_

Independent Assortment

F1 generation = heterozygous dominant with round yellow peas

RRYY rryy

RrYy

Independent Assortment

• Circle the letter of the phenotypes that Mendel would expect to see if genes segregated independently.

• a. round and yellow• b. wrinkled and green• c. round and green• d. wrinkled and yellow

Overall concept:

Q: What did Mendel observe in the F2 offspring that showed him that the alleles for seed shape segregate independently of those for seed color?

A: He observed F2 offspring that had combinations of phenotypes—and therefore combinations of alleles—not found in either parent.

2-Factors:Sample Problem

• Dihybrid Cross

In the breeding season, male Anole lizards court females by bobbing their heads up and down while displaying a colorful throat patch. Assume for this question that both males and females bob their heads and have throat patches. Assume also, that both traits are controlled by single locus genes on separate chromosomes. Now, suppose that anoles prefer to mate with lizards who bob their heads fast (F) and have red throat patches (R) and that these two alleles are dominant to their counterparts, slow bobbing and yellow throats. A male lizard heterozygous for head bobbing and homozygous dominant for the red throat patch mates with a female that is also heterozygous for head bobbing but is homozygous recessive for yellow throat patches

Dihybrid Cross Problem #1:

a) How many of the F1 offspring have the preferred fast bobbing / red throat phenotype (assume 16 young)?

b) What percentage of the offspring will lack mates because they have both slow head bobbing and yellow throats?

c) What percentage of the offspring will havetrouble finding mates because because they lackone of the dominant traits?

a) 12 b) 0% c) 25%