Unit 5: Heredity #2

What are true-breeding parents called in a genetic cross?

The P (parental) generation

What is the F1 generation?

The first filial generation, offspring of the P generation

What is the F2 generation?

The second filial generation, offspring of the F1 generation

What does Mendel’s law of segregation state?

Two alleles for each trait separate during gamete formation

What does the law of independent assortment state?

Each pair of alleles segregates independently during gamete formation

During what phase of meiosis does independent assortment occur?

Metaphase I

What are alternative versions of a gene called?

Alleles

How many alleles does each sexually reproducing organism inherit per gene?

Two (one from each parent)

What is a homozygous organism?

An organism with two identical alleles for a gene (RR or rr)

What is a heterozygous organism?

An organism with two different alleles for a gene (Rr)

What is a phenotype?

The physical expression of a trait

What is a genotype?

The genetic makeup of an organism

What is a testcross used for?

To determine if an organism showing a dominant trait is homozygous dominant (RR) or heterozygous (Rr)

What type of individual is used in a testcross?

A homozygous recessive (rr) individual

What is a monohybrid cross?

A cross that studies one trait

What is a dihybrid cross?

A cross that studies two traits

What is complete dominance?

The heterozygote and homozygous dominant individual are indistinguishable in phenotype (Yy = YY)

What is incomplete dominance?

The heterozygote has an intermediate phenotype (e.g., red + white = pink)

What is codominance?

Both alleles affect the phenotype in different but equal ways (AB blood type)

What are multiple alleles?

When a gene has more than two allelic forms (blood types: IA, IB, i)

What is polygenic inheritance?

A single trait is affected by multiple genes (height, skin color)

What is phenotypic plasticity?

The environment influences phenotype (sun exposure affecting skin tone)

What is a pedigree?

A diagram showing inheritance patterns across generations

How are males and females represented in pedigrees?

Males: squares, Females: circles

What does a shaded shape in a pedigree indicate?

The individual expresses the trait

What is a recessively inherited disorder?

A disorder that requires two copies of a defective gene (aa)

What are three examples of recessively inherited disorders?

Cystic fibrosis, Tay-Sachs disease, Sickle-cell disease

What is a dominantly inherited disorder?

A disorder that requires only one copy of a defective gene (A_)

What are two examples of dominantly inherited disorders?

Achondroplasia (dwarfism), Huntington’s disease

What is amniocentesis?

A procedure that removes amniotic fluid to test for genetic disorders

What is chorionic villus sampling (CVS)?

A procedure that removes placental cells for karyotyping

How can fetal DNA be analyzed noninvasively?

By isolating fetal DNA from the mother’s blood