Bio test pheno/genotype

What kind of cross typically produces a 3:1 phenotypic ratio?

A monohybrid cross between two heterozygotes (Aa × Aa), assuming complete dominance.

What kind of cross typically produces a 9:3:3:1 phenotypic ratio?

A dihybrid cross between two individuals heterozygous for both independently assorting genes (AaBb × AaBb), assuming complete dominance.

What is a phenotype?

An organism's observable traits or characteristics.

What is a genotype?

An organism's allele combination or genetic makeup.

What does homozygous mean?

Having two identical alleles for a gene (AA or aa).

What does heterozygous mean?

Having two different alleles for a gene (Aa).

What are alleles?

Alternative forms of the same gene.

In a typical Mendelian monohybrid cross, which generation is completely heterozygous?

The F1 generation, when true-breeding parents with contrasting alleles (AA × aa) are crossed; all offspring are Aa.

What is Mendel's law of segregation?

The two alleles for a gene separate during gamete formation, so each gamete receives one allele.

What is Mendel's law of independent assortment?

Alleles of different genes assort independently into gametes when the genes are unlinked or sufficiently far apart on a chromosome.

What are the genotypes of the F1 offspring in a monohybrid cross between true-breeding parents (AA × aa)?

All F1 offspring are heterozygous (Aa).

What is the blending theory of inheritance?

The outdated idea that parental traits mix together in offspring and cannot be separated again.

What is nondisjunction?

The failure of chromosomes or sister chromatids to separate properly during cell division, which can produce cells or gametes with abnormal chromosome numbers.

What is a karyotype?

A display of an individual's chromosomes arranged in homologous pairs, generally by size, shape, and banding pattern.

How are chromosomes arranged in a karyotype?

In homologous pairs, usually ordered from largest to smallest, with the sex chromosomes shown at the end.

What is a polygenic trait?

A trait influenced by alleles of multiple genes, often producing a range of phenotypes.

What is a chromosomal inversion?

A chromosome segment breaks off, flips around, and reattaches in reverse orientation.

What is a chromosomal translocation?

A chromosome segment moves to a different, nonhomologous chromosome.

What is a chromosomal deletion?

A chromosome segment is lost.

What is a chromosomal duplication?

A chromosome segment is copied, so extra genetic material is present.

What are common characteristics of X-linked traits?

The gene is on the X chromosome; X-linked recessive traits are often more common in males because males typically have only one X chromosome.

What is epistasis?

An interaction in which an allele of one gene affects or masks the expression of another gene.

What is pleiotropy?

When one gene affects multiple traits.

What is incomplete dominance?

Neither allele completely masks the other in a heterozygote, so the phenotype is intermediate between the two homozygotes.

What causes Down syndrome?

Usually an extra copy of chromosome 21 (trisomy 21), often due to nondisjunction.

What causes sickle cell disease?

Variants in the HBB gene that cause hemoglobin S; the disease is typically inherited in an autosomal recessive pattern.

What causes hemophilia?

Commonly, variants in clotting-factor genes such as F8 (hemophilia A) or F9 (hemophilia B); classic forms are X-linked recessive.

What causes cystic fibrosis?

Variants in the CFTR gene; it is inherited in an autosomal recessive pattern.

What is the typical karyotype for Turner syndrome?

45,X (one X chromosome; sometimes mosaic forms occur).

What is the typical karyotype for Klinefelter syndrome?

47,XXY.

What is the typical karyotype for Jacobs syndrome?

47,XYY.

What is a pedigree chart?

A family diagram that uses standardized symbols to show how a trait appears across generations.

What do common pedigree symbols mean?

Square = male; circle = female; shaded symbol = affected individual; horizontal line = mating/parents; vertical line = offspring.

What is often taught as the most common genetic disease among people of European ancestry in introductory biology?

Cystic fibrosis is commonly described that way in many U.S. introductory biology courses.

How is the ABO blood type inherited?

By three common alleles: IA, IB, and i. IA and IB are codominant, and both are dominant over i.

What genotype(s) can produce blood type A?

IAIA or IAi.

What genotype(s) can produce blood type B?

IBIB or IBi.

What genotype produces blood type AB?

IAIB.

What genotype produces blood type O?

ii.

How is Rh-positive blood type inherited in the simplified model commonly taught in biology?

Rh-positive is usually treated as dominant (D_), while Rh-negative is recessive (dd).

What causes Tay-Sachs disease, and how is it inherited?

Variants in the HEXA gene cause Tay-Sachs disease; it is inherited in an autosomal recessive pattern.

What causes phenylketonuria (PKU), and how is it inherited?

Most classic PKU is caused by PAH gene variants and is inherited in an autosomal recessive pattern.

What causes neurofibromatosis type 1, and how is it inherited?

Variants in the NF1 gene cause NF1; it is typically inherited in an autosomal dominant pattern.

How do you interpret a pedigree chart?

Check which individuals are affected in each generation; note whether males and females are affected; look for father-to-son transmission.

Why is pattern baldness often more common or pronounced in males?

It is influenced by genes and androgens such as testosterone and dihydrotestosterone (DHT).

How do you set up a dihybrid cross?

Write each parent's genotype for both genes, list possible gametes, then combine gametes in a 4 × 4 Punnett square.

What phenotypic ratio is expected from AaBb × AaBb when the genes assort independently and show complete dominance?

9:3:3:1.

What is the difference between genotype and phenotype?

Genotype is the allele combination; phenotype is the observable trait produced by genotype and environmental influences.