Exam II Flashcards
What is a cross?
A mating that produces offspring.
Usually done multiple times.
What is a single-factor cross?
A cross involving one character controlled by one gene.
What is the parental (P) generation?
The first two individuals used for crossing. One individual will be homozygous dominant and the other will be homozygous recessive.
What is the first filial (F1) generation?
The offspring of the P generation. All offspring will be heterozygous.
What is the second filial (F2) generation?
The offspring of the F1 generation.
What is the difference between an autosome and a sex chromosome?
An autosome does not determine the genetic sex of an individual.
Sex chromosomes determine the genetic sex.
What are autosomal traits?
Traits produced by genes on autosomes.
What is Mendel’s Law of Segregation?
Basically “one allele of each autosomal gene is inherited from each parent.”
A parent has two alleles for each autosomal gene, which are separated from meiosis.
Each gamete has one of those alleles; offspring receive only one from each parent.
What is true-breeding?
A term meaning that an individual has a homozygous genotype.
How do you write out a potential cross?
__ __ x __ __
Punnett square.
yeah?
For incomplete dominance, what is a test-cross and what is it used for?
A cross between an individual with the dominant phenotype and one with the recessive phenotype. Test-crosses are used to distinguish the two genotypes
When is the 2:1 phenotypic ratio observed and why?
A 2:1 phenotypic ratio is observed whenever there is a lethal allele present. Typically, individuals that are homozygous for the lethal allele will not be alive, not contributing to the observations.
What is a sex-linked trait?
Traits produced by genes on sex chromosomes.
Why is the inheritance of sex-linked traits different from that of autosomal traits?
The two sexes, male and female, have different combinations of sex chromosomes.
Describe how males and females differ in the sex chromosome combinations.
Males: XY
Females: XX
Why aren’t the X and Y chromosomes considered a homologous pair?
The X and Y chromosomes are not considered homologous pairs because they have different sets of genes.
What are pseudoautosomal genes?
Genes found on BOTH X and Y genes.
What are holandric genes?
Genes found only on the Y chromosome.
What are X-linked genes?
Genes found only on the X chromosome.
Genes in which category can be found on the X chromosome?
Pseudoautosomal and x-linked genes.
Genes in which category can be found on the Y chromosome?
Pseudoautosomal and holandric genes.
Which category contains the most genes?
Pseudoautosomal genes contain the most genes.
Define the term hemizygous.
A genotype that consists of only one allele.
What do the products of holandric genes do?
The product of holandric genes produces the trait of “maleness.”
Most important holandric gene: Sex-determining Region Y (SRY) gene.
When does sexual differentiation of the human gonads begin?
Sexual differentiation begins at 7 weeks.
Describe male sex determination during human embryonic development.
After 7 weeks of embryonic development, if the embryo is male, SRY will begin producing TDF.
Explain the role of the SRY gene and its product TDF during male sex determination.
SRY produces Testis-Determining Factor (TDF).
TDF activates genes involved in testis formation and represses the ones for ovary production.
What is XY-sex reversal, and how is it produced?
XY-sex reversal is when an individual presents a female phenotype but is genotypically male.
Occurs at birth.
It is caused by null alleles of the SRY gene.
Which sex is more likely to inherit X-linked hypophosphatemia? Why?
Females are more likely to inherit X-linked hypophosphatemia. This is because the mutant, disease causing-allele is dominant (XH) and only found in X chromosomes.
Which sex is more likely to inherit the red-green colorblindness trait? Why?
Males are more likely to inherit colorblindness. This is because the mutant allele is recessive and found only on the X chromosome. Females would have to be homozygous recessive to be colorblind while males simply need one recessive X allele.
What is a two-factor cross?
Any cross involving two genes.
AKA dihybrid cross.
Two-factor crosses and selective breeding?
Humans select two desirable traits for certain organisms.
“One character” is composed of multiple characters.
Think coat colors in cats (5 genes, each affecting different aspects of coat colors).
Explain the difference between linked and unlinked genes.
Linked: genes on the same chromosome.
Unlinked: genes that are on different chromosomes.
What are the shape and colors of the seeds in the common garden pea?
Color: Yellow (G), green (g)
Shape: Round (R), wrinkled (r)
What is gene interaction?
Two genes working together to produce a single character.
What are the four comb shapes in chickens?
Walnut
Rose
Pea
Single
What two genes affect the comb shape in chickens?
Rose gene
Pea gene
What is the dominant and recessive allele for the comb shape in chickens?
Rose gene = Dom: R; Rec: r
Pea gene = Dom: P; Rec: p
Genotypes for walnut combs in chickens.
At least ONE dominant allele for both rose and pea genes.
RRPP, RrPp, RrPP, RRPp
Genotypes for rose combs in chickens.
At least ONE dominant allele for rose gene and homozygous recessive for pea gene.
Rrpp, RRpp
Genotypes for pea combs in chickens.
At least ONE dominant allele for pea gene and homozygous recessive for rose gene.
rrPP, rrPp
Genotypes for single combs in chickens.
Homozygous recessive.
rrpp
