Theoretical Genetics

Genetic Terms:P = parental generation of a crossF1 = the first generation after the parental

(the results of the first cross)F2 = a cross between F1 individuals yields F2

Genotype – the alleles of an organism as inherited from the parents

Phenotype – the characteristics of the organism due to the interaction of the genotype and the environment

Homozygous – having two identical alleles of a gene

Heterozygous – having two different alleles of a gene

AA aa are homozygousAa are heterozygous

Dominant allele – expressed phenotypically whether it is homozygous or heterozygous

Recessive allele – expressed phenotypically only in the homozygous state

Capital letters are used to represent the dominant allele

Lower case for the recessiveDominant allele always listed first

Codominant alleles – pairs of alleles that both affect the phenotype when present in the heterozygous state

Locus – the particular position of a gene on homologous chromosomes

Carrier – an individual that has one copy of a recessive gene that causes a genetic disease in individuals that are homozygous for the gene

Test cross – checking the genotype of an individual by crossing it with a known homozygous recessive

B? X bbThe percentage phenotype give answer

Determine genotypes and phenotypes using a punnett square.

The possible gametes of each individual are determined.

Each gamete will have one of the two alleles of the parent.

Generate a punnett square and write the alleles for parent 1 on the left side of the Punnett square.

Place the alleles for parent 2 above the square

Fill the squares for each parent

The odds of 2 or more independent events occurring together is the product of each independent event.

In a cross between pea plants that are heterozygous for flower color (Pp), what is the probability that the offspring will be homozygous recessive?

½ x ½ = ¼

Probability that events that can occur in 2 or more different ways will occur, is the sum of the separate problems.

In a cross between pea plants that are heterozygous for flower color (Pp), what is the probability of the offspring being heterozygous?

¼ + ¼ = ½

The odds of two different traits occurring together in the same offspring is the product of each independent trait occurring in the offspring.

In which phase of meiosis does this event occur?

What assumption did Mendel make for this law to work?

Some traits have more than two allelesCoat color in rabbits and catsDrosophila wingsHuman blood types

Women – homozygous XXMen – heterozygous XY23rd pair chromosomesDimorphic SRY gene on Y determines Presence of male features

Mothers can only contribute X chromosomeFathers can contribute either X or Y thus

determine gender of child50% chance boy, 50% chance girl foreach fertilization event

Nile crocodiles sand temperature around the eggs during incubation affects gender - higher temperatures favor males

Turtles and lizards high temperatures favor females

Many fish are hermaphrodites and under certain environmental conditions will switch gender

http://www.ornl.gov/hgmis/posters/chromosome/chooser.shtml

X chromosome much larger than YMany genes found on X that are not present

on Y

Genes on X with no counterpart on Y are called sex linked genes

Often affect one gender more than anotherColor Blindness and Hemophilia

Caused by mutant gene recessiveEncodes either clotting factor Vlll = h-AOr clotting factor lX = h-BCarried on X chromosomeHeterozygous will clot normally as their good

copy of gene produces enough clotting factorIf only mutant gene copy present will suffer

from excessive bleeding

Red-green color blindness carried on XBlue color sensitivity is carried on

chromosome 7 and inherited as any autosomal gene

4 Sex-Linked Traits: 1. Normal Color Vision: A: 29, B: 45, C: --, D: 26 2. 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

Females can be homozygous or heterozygous for sex- linked traits

Females with one or two dominant alleles for a sex linked trait will not exhibit the trait

Females that are heterozygous for sex-linked traits are called carriers

Only females can pass on sex-linked traits to their sons

• The calico cat is the result of multiple alleles on the X chromosome combines with X inactivation.

• One allele causes orange fur and the other causes black fur.

• The male cat will be either orange or black.• Only a heterozygous female will be calico

with regions that are orange and regions that are black based on the X inactivation

Predict genotype and phenotype using Punnett Squares for all of the inheritance patterns mentioned above

Deduce the genotype and phenotype of individuals in a pedigree chart