genetics Flashcards

Question

what tests can identify carriers?

Answer 1

fetal testing (screening and diagnostic testing), imaging and blood test screening, diagnostic (amniocentesis detects serious recessive disease, chorionic villus sampling), newborn screening

Answer 2

only one mutated allele needed. there are lots of genes on X chromosome. Y chromosome = "genetic wasteland", much smaller than X. males are hemizygous for sex-linked genes (an individual who has only one copy of a gene, rather than the usual two)

Answer 3

- Recessive deleterious alleles (aa) can persist because carriers (Aa) do not express the harmful trait. - Late-Onset Disorders Example: Huntington’s disease symptoms develop after 30-40 years, allowing affected individuals to pass on the allele before symptoms appear. - Mutation and New Introductions Harmful alleles can continuously arise due to random mutations. Even if selection removes some, mutations reintroduce them into the gene pool. - Balancing Selection When natural selection maintains genetic variation in a population because different alleles provide advantages in different conditions. Example: The G6PD deficiency allele is common in malaria-endemic regions because it reduces malaria severity.

Answer 4

- reduces random error, increases accuracy - captures genetic variatoin - accounts for outside influences

Answer 5

In an Individual: - Each person has two alleles for a given gene (one from each parent). - Example: For the ABO blood group, an individual can have only two alleles (e.g., A and O). In a Population: - A population can have multiple alleles for the same gene, beyond just the two found in any individual. - Example: The ABO blood group has three alleles (A, B, and O) present in the population, though an individual only inherits two.

Answer 6

Complete Dominance - One allele completely masks the effect of the other. - Heterozygotes (Aa) express only the dominant trait (A). - Example: Mendelian pea plants – Purple (A) is dominant over white (a), so Aa = purple flowers. Codominance - Both alleles are fully expressed in heterozygotes. - No blending—both traits appear simultaneously. - Example: AB blood type – A and B alleles are both equally expressed, resulting in AB blood. Incomplete Dominance - Blending of traits occurs in heterozygotes. - The heterozygous phenotype is intermediate between the two homozygous phenotypes. - Example: Red (RR) × White (WW) snapdragons → Pink (RW) offspring.

Answer 7

1. Inheritance Pattern - The ABO blood group follows codominant inheritance. - The ABO gene (on chromosome 9) has three alleles: Iᴬ (produces A antigen) Iᴮ (produces B antigen) i (produces no antigen, O type) - Iᴬ and Iᴮ are codominant, meaning both are expressed if inherited together (AB blood type). - i is recessive, so individuals with ii have blood type O. Genotype Phenotype (Blood Type) IᴬIᴬ or Iᴬi A IᴮIᴮ or Iᴮi B IᴬIᴮ AB ii O 2. Molecular Basis - The ABO gene encodes an enzyme (glycosyltransferase) that modifies sugar molecules on red blood cell surfaces. - Iᴬ allele → Adds N-acetylgalactosamine (A antigen). - Iᴮ allele → Adds galactose (B antigen). - i allele → Non-functional enzyme, no sugar modification (O blood type has no antigens). 3. Clinical Relevance - ABO blood type is crucial for blood transfusions (incompatible transfusions cause immune reactions). - Universal Donor: Type O (no antigens). - Universal Recipient: Type AB (has both A & B antigens, so no antibodies against either). - This system demonstrates Mendelian inheritance, codominance, and biochemical differences at the molecular level.

Answer 8

1. What is an Allelic Series? An allelic series refers to multiple alleles of a single gene that have a hierarchy of dominance relationships. Some alleles may be completely dominant, recessive, or show partial dominance over others. 2. Example of an Allelic Series One classic example is the C gene in rabbit coat color, which has multiple alleles with a dominance hierarchy: C (full color) > cʰ (Himalayan) > cʙ (chinchilla) > c (albino) C is dominant to all other alleles. cʰ is dominant to cʙ and c, but recessive to C. c is fully recessive to all other alleles. 3. An Allele Can Be Both Dominant and Recessive A single allele can be dominant to one allele but recessive to another, depending on the combination. Example: In the rabbit coat color allelic series: cʰ (Himalayan) is dominant over c (albino) → cʰc = Himalayan cʰ (Himalayan) is recessive to C (full color) → Ccʰ = full color This concept helps explain how multiple traits arise from a single gene, leading to variation within a species.

Answer 9

Pleiotropy: One gene, many traits Polygenic inheritance: Many genes, one trait

Answer 10

- Sex-linked traits depend on sex chromosomes (X or Y), while autosomal traits are on non-sex chromosomes. - Males are more affected by X-linked recessive traits since they only have one X chromosome. - Autosomal traits affect both sexes equally.

Answer 11

1. Sex Determination (SRY Gene) The Y chromosome contains the SRY gene (Sex-determining Region Y), which is responsible for initiating the development of male characteristics. The SRY gene triggers the development of testes from the undifferentiated gonads, which leads to the production of male hormones (androgens) like testosterone. Testosterone further drives the development of male sexual characteristics, such as male reproductive organs and secondary sexual traits (e.g., body hair, deep voice). 2. Spermatogenesis The Y chromosome contains genes crucial for sperm production. These genes are involved in the formation and function of the testes, which are essential for the production of sperm (the male gametes). Mutations or deletions of key genes on the Y chromosome can lead to infertility. 3. Inheritance The Y chromosome is passed from father to son and is inherited in a paternal lineage. This allows it to be used in tracing male ancestry through generations. 4. Dosage Compensation Since males only have one X chromosome and one Y chromosome, they lack a second X chromosome to compensate for potential genetic imbalances. This makes the X chromosome in males highly significant for gene expression and functioning, while the Y chromosome mainly influences male sex characteristics.

Answer 12

regulation of chromatin structure - histone modifications and DNA methylation - epigenetic inheritance (methyl-group containing compounds can change traits, mutations to DNA are permanent but modifications to chromatin are reversible)

Answer 13

control elements (segments of noncoding DNA that serve as binding sites for the proteins called transcription factors)