Relate Genes to Trait Inheritance - Biology

What is a dominant allele in simple Mendelian inheritance?

An allele expressed in the heterozygous phenotype. Usually written in uppercase and masks recessive alleles.
In X-linked inheritance, which parent passes an X chromosome to all daughters?

The father. All daughters inherit father's X and one maternal X chromosome.
What is an autosomal recessive inheritance pattern typically characterized by in pedigrees?

Trait can skip generations; affected individuals may have unaffected parents. Recessive traits often appear to skip generations in pedigrees.
What is a locus?

A gene's specific physical location on a chromosome. Each gene occupies a specific position on its chromosome.
What is an autosome?

Any chromosome that is not a sex chromosome. Non-sex chromosomes that follow standard Mendelian inheritance patterns.
What is a carrier in autosomal recessive inheritance?

A heterozygote with the recessive allele but no disease phenotype. Has one recessive allele but shows the dominant phenotype.
State the formula for number of gamete types from a genotype with $n$ heterozygous loci.

$2^n$ . Where $n$ is the number of heterozygous gene pairs.
What is multiple alleles inheritance?

A gene has more than two alleles in the population. Population contains additional allelic variants beyond two.
What fraction of offspring are expected to be heterozygous in $Aa \times Aa$ ?

$\frac{1}{2}$ . Half the offspring inherit one allele from each parent.
What are the possible genotypes for blood type A in the ABO system?

$I^AI^A$ or $I^Ai$ . Type A can be homozygous or heterozygous with $i$ allele.
What is codominance?

Both alleles are fully expressed in the heterozygote. Both traits appear simultaneously without blending.
What is a test cross used to determine?

Whether a dominant-phenotype individual is homozygous or heterozygous. Cross with homozygous recessive reveals the unknown genotype.
Which term describes a cross involving one gene with two alleles?

Monohybrid cross. Focuses on inheritance of a single trait.
What is a Punnett square used to predict?

Expected offspring genotype and phenotype probabilities. A grid showing all possible offspring combinations from a cross.
Which human blood group system demonstrates multiple alleles and codominance?

ABO blood group. Classic example with three alleles showing both dominance patterns.
What is epistasis?

One gene masks or modifies the expression of another gene. Gene interactions where one gene affects another's expression.
What is the expected phenotypic ratio from $AaBb \times AaBb$ with independent assortment?

$9:3:3:1$ . Classic ratio for two independent traits with complete dominance.
What fraction of offspring are expected to be homozygous recessive in $Aa \times Aa$ ?

$\frac{1}{4}$ . Only one-fourth inherit both recessive alleles.
What is a gene in the context of inheritance of traits?

A DNA segment that encodes a functional product affecting traits. The unit of heredity that codes for proteins or RNA molecules.
Identify the genotype of the tester parent in a standard Mendelian test cross.

Homozygous recessive. The known genotype that reveals the unknown parent's genetics.
What is a sex-linked trait?

A trait controlled by a gene located on a sex chromosome. Inheritance patterns differ from autosomal traits due to sex chromosomes.
What fraction of offspring are expected to show the dominant phenotype in $Aa \times Aa$ ?

$\frac{3}{4}$ . Includes both homozygous and heterozygous dominant genotypes.
What is the expected phenotypic ratio in incomplete dominance for $Aa \times Aa$ ?

$1:2:1$ . Each phenotype is distinct, including the intermediate form.
What is a polygenic trait?

A trait influenced by multiple genes, often with continuous variation. Multiple genes contribute additive effects to phenotype expression.
What process can separate linked alleles and create recombinant gametes?

Crossing over during meiosis. Recombination frequency depends on physical distance between linked genes.
What genotype produces blood type AB in the ABO system?

$I^AI^B$ . Codominance allows both A and B antigens to be expressed.
How many different gamete types can $AaBb$ produce by independent assortment?

$4$ . Each heterozygous gene contributes two possible alleles to gametes.
What is a Y-linked (holandric) trait?

A trait controlled by a gene on the Y chromosome, passed father to son. Exclusively paternal inheritance through the male lineage only.
In X-linked inheritance, which parent always passes an X chromosome to sons?

The mother. Fathers pass Y chromosomes to sons, X chromosomes come from mothers.
What is incomplete dominance?

Heterozygote shows an intermediate phenotype. Neither allele is completely dominant over the other.
How many different gamete types can $AaBbCc$ produce (assume independent assortment)?

$8$ . Three heterozygous genes: $2^3 = 8$ different combinations.
What is the expected genotypic ratio from $Aa \times Aa$ ?

$1:2:1$ ( $AA:Aa:aa$ ). Shows the actual allele combinations in offspring.
What is a phenotype?

The observable trait produced by genotype and environment. The physical expression of genes influenced by environmental factors.
In a test cross, dominant phenotype parent yields $1:1$ phenotypes; what is its genotype?

Heterozygous. Mixed offspring ratios indicate the parent has both allele types.
Which sex chromosome carries most human sex-linked genes?

The X chromosome. Contains more genes than the smaller Y chromosome.
What fraction of offspring are expected to show the recessive phenotype in $Aa \times Aa$ ?

$\frac{1}{4}$ . Only homozygous recessive individuals show the recessive trait.
What does it mean if an organism is heterozygous for a gene?

It has two different alleles at that locus. The alleles differ, written as $Aa$ or $Bb$ .
Why are X-linked recessive traits more common in males than females?

Males have one X chromosome, so one recessive allele is expressed. No second X chromosome to mask recessive alleles in males.
What is linked inheritance?

Genes close together on the same chromosome tend to be inherited together. Physical proximity reduces crossing over frequency between genes.
What is an autosomal dominant inheritance pattern typically characterized by in pedigrees?

Trait appears in every generation; affected individuals often have an affected parent. Dominant traits typically show vertical transmission through generations.
In a test cross, all offspring show dominant phenotype; what is the parent genotype?

Homozygous dominant. Uniform dominant offspring indicate parent lacks recessive alleles.
What is Mendel's law of segregation?

Allele pairs separate during gamete formation. Each gamete gets only one allele from each pair.
Identify the required genotype for a recessive phenotype to be expressed.

Homozygous recessive (two recessive alleles). Recessive traits need both alleles to be recessive for expression.
What is Mendel's law of independent assortment?

Alleles of different genes assort independently in gametes. Different traits are inherited separately if genes aren't linked.
What is an allele?

An alternative version of a gene at the same locus. Different forms of the same gene, like $A$ and $a$ .
What is pleiotropy?

One gene affects multiple distinct phenotypic traits. Single genes can influence seemingly unrelated characteristics.
What is a genotype?

The allele combination an organism has for a gene. The genetic makeup, typically written as letter combinations like $AA$ or $Aa$ .
What genotype produces blood type O in the ABO system?

$ii$ . Homozygous recessive produces no A or B antigens.
Which term describes a cross involving two different genes?

Dihybrid cross. Examines inheritance patterns of two separate traits simultaneously.
What is a recessive allele in simple Mendelian inheritance?

An allele expressed only when homozygous. Usually written in lowercase and requires two copies for expression.
What is the expected phenotypic ratio from $Aa \times Aa$ with complete dominance?

$3:1$ (dominant:recessive). Classic ratio when dominant allele masks recessive in heterozygotes.
What does it mean if an organism is homozygous for a gene?

It has two identical alleles at that locus. Both alleles are the same, either $AA$ or $aa$ .

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