Biology CPE: Gentics Part 1-3 Test - Roberts

Heredity

The passing of traits from parent to offspring

Genetics

The study of heredity

Characteristic

An inherited feature (e.g., flower color)

Trait

A specific version of a characteristic (e.g., purple flower)

Gene

A piece of DNA that codes for a protein (a unit of heredity)

Locus

The specific location of a gene on a chromosome

Allele

A version of a gene (e.g., R or r)

Homozygous

Two identical alleles for a gene (RR or rr); 'purebred'

Heterozygous

Two different alleles for a gene (Rr); 'hybrid'

Genotype

The combination of alleles for a gene (e.g., Rr, rr, RR)

Phenotype

The physical expression of a trait (e.g., round peas)

Dominant Allele

An allele that shows in the phenotype if present (uppercase letter)

Recessive Allele

An allele that shows in the phenotype only if both alleles are recessive (lowercase letter)

Law of Segregation

Each organism inherits two copies of a gene and passes on only one copy in gametes

Law of Independent Assortment

Allele pairs separate independently during gamete formation (traits are inherited separately)

Punnett Square

A grid used to predict all possible genotypes of offspring from a cross

Monohybrid Cross

A genetic cross that examines the inheritance of one trait

Dihybrid Cross

A genetic cross that examines the inheritance of two different traits

Ratio

The comparison of the number of different outcomes in a genetic cross

Genotypic Ratio

Comparison of genetic combinations (e.g., 1 RR: 2 Rr: 1 rr)

Phenotypic Ratio

Comparison of physical traits (e.g., 3 round: 1 wrinkled)

Mendel's 3 Conclusions

Traits are inherited as units; organisms inherit 2 alleles per gene; only 1 allele is passed on in gametes

Self-fertilization

The eggs of a plant are fertilized by sperm from the same plant

Cross-fertilization

The eggs of one plant are fertilized by sperm from a different plant

F1 Generation

First generation of offspring from a cross (all dominant phenotype if purebreds are crossed)

F2 Generation

Second generation from self-fertilization of F1; reveals hidden recessive traits (3:1 ratio)

What happens in a test cross?

You cross an unknown dominant organism with a homozygous recessive to figure out its genotype

If all offspring are dominant in a test cross

Then the unknown genotype is homozygous dominant

If some offspring are recessive in a test cross

Then the unknown genotype is heterozygous

Gametes from RR

One gamete type: R

Gametes from Rr

Two gamete types: R and r

Homozygous dominant x Homozygous recessive

Genotype = 100% Rr; Phenotype = 100% dominant

Heterozygous x Heterozygous

Genotype = 1:2:1; Phenotype = 3:1

Homozygous dominant x Heterozygous

Genotype = 1:1 (RR:Rr); Phenotype = 100% dominant

Homozygous recessive x Heterozygous

Genotype = 1:1 (Rr:rr); Phenotype = 1:1 (dominant:recessive)

What are the alleles for pea color?

Y (yellow), y (green)

What are the alleles for pea shape?

R (round), r (wrinkled)

How many boxes in a dihybrid Punnett square?

16

Dihybrid phenotypic ratio

9:3:3:1 (Dom/Dom : Dom/Rec : Rec/Dom : Rec/Rec)

What does a 9:3:3:1 ratio represent?

9 yellow/round, 3 yellow/wrinkled, 3 green/round, 1 green/wrinkled

What is a genome?

All of an organism's genetic material

Which genotype produces a recessive phenotype?

Homozygous recessive (e.g., rr)

Can heterozygous organisms show the dominant trait?

Yes, because one dominant allele is enough for expression

Are all traits simple dominant-recessive?

No, many traits occur in a range (complex inheritance)