Inheritance (College Board AP® Biology): Flashcards

• Males are represented by squares

• Females are represented by circles

Horizontal lines link individuals that have produced children; vertical lines show the relationship between parent and child.

To compare observed results with expected results (such as those predicted by Mendel's laws) and determine whether the difference is statistically significant or due to chance.

In a chi-square test, the degrees of freedom equal the number of classes minus one.

True.

A chi-square value greater than or equal to the critical value means the difference is significant, so the null hypothesis is rejected.

Gene linkage is when genes are located on the same chromosome, so they tend to be inherited together rather than assorting independently as Mendel's laws predict.

Genes located on the same chromosome are described as being genetically linked.

By using the probability that the linked genes are inherited together (segregate together during meiosis). This calculation is called gene mapping (genetic mapping).

Codominance is when the phenotypes from both alleles in a heterozygote are fully and simultaneously expressed, so the heterozygote has a different phenotype from either homozygote (e.g. AB blood group).

Incomplete dominance is when neither allele can mask the other, so the heterozygote shows a blended (intermediate) phenotype between the two homozygotes (e.g. a pink flower from red and white alleles).

True.

Incomplete dominance gives a blend (e.g. pink), while codominance shows both phenotypes together (e.g. speckled chickens, AB blood).

Sex-linked trait is a trait determined by a gene on a sex chromosome (X- or Y-linked), so its pattern of inheritance differs between XX and XY individuals.

An XY individual has only one copy of an X-linked gene, so a single recessive allele is expressed. An XX individual has two copies, so a second dominant allele can mask the recessive one, making them a carrier instead.

False.

Some species use other systems, such as ZW chromosomes in birds and haplodiploidy in bees (females diploid from fertilized eggs, males haploid from unfertilized eggs).

Pleiotropy is when the expression of a single gene results in multiple traits or effects; because they stem from one gene, these traits do not segregate independently.

Sickle cell anemia: a single gene (HBB) produces several effects, including anemia, pain crises, spleen damage, and malaria resistance.

(Cystic fibrosis is another example: thick lung mucus, pancreatic insufficiency, and salty sweat.)

Non-nuclear inheritance is the inheritance of traits determined by DNA in organelles such as mitochondria and chloroplasts, rather than by nuclear chromosomes, so it does not follow simple Mendelian rules.

In animals, mitochondria are transmitted by the egg cell and not by sperm, so mitochondrial DNA (and the traits it codes for) is inherited through the maternal line.

Because chloroplasts and mitochondria are randomly assorted to gametes and daughter cells, the traits they determine do not follow simple Mendelian rules.

Phenotypic plasticity is the ability of a single genotype to produce different phenotypes in response to different environmental conditions.

Differences in environmental conditions influence gene expression, so the same fixed genotype can be expressed as different phenotypes.

False.

The genotype remains fixed throughout the organism's lifetime; only the way the phenotype is expressed varies with the environment.

Environmental stimuli such as light, drugs, and hormones can alter the levels of regulatory proteins or transcription factors, changing gene expression.

Human height is influenced by both genetics and environmental factors; poor nutrition can limit growth even when the genotype favors tall stature.

In the Hydrangea genus, flowers are blue in acidic soil and pink in alkaline soil, showing that flower color varies with soil pH.

Daylength (the amount of light received per day). Shorter winter days stimulate growth of white hair, while longer summer days lead to brown or gray fur.

True.

Eggs incubated at cool (22°C or lower) or hot (28°C or above) temperatures hatch as females, while intermediate temperatures produce predominantly males.

UV radiation activates genes involved in melanin synthesis, increasing melanin production and causing darker pigmentation (e.g., tanning) that protects against DNA damage.

When yeast cells detect pheromones from the opposite mating type, they alter gene expression and produce complementary signals to ensure successful mating.

True.

Temperature is an environmental factor that can affect gene expression, as seen in temperature-dependent sex determination in reptiles.

Environmental stressor is an external environmental factor (such as UV radiation) that can directly influence gene expression and shape protective phenotypic traits.