Genetics and Chromosome Numbers

Chromosome Numbers and Reproduction

• Gametes have half the chromosomes of somatic cells (haploid). For example, if an organism has 46 total chromosomes, each gamete will have 23.
• Donkeys have 62 chromosomes (31 pairs). A donkey zygote has 62 chromosomes formed by the fusion of gametes, each with 31 chromosomes.
• Mules are infertile due to a hybrid combination of horse (64 chromosomes) and donkey (62 chromosomes). This results in 63 chromosomes, leading to pairing issues during meiosis, causing infertility.

Genetics Terms

• Homozygous: An organism with two identical alleles for a trait (e.g., AA or aa).
• Heterozygous: An organism with two different alleles for a trait (e.g., Aa).
• Genotypes: Homozygous genotypes include AA or aa, while heterozygous genotypes are represented as Aa.
• Recessive traits require both alleles to be recessive (aa) for expression, whereas dominant traits only require one dominant allele to be expressed.

Traits, Mutations, and Sex-Linked Traits

• Co-dominant traits: Both alleles are fully expressed in the phenotype. In blood types, IAIB genotype results in both A and B antigens.
• Sex-linked traits (X-linked): Females need two copies of the allele for expression (XX). Males (XY) only need one copy.
• Klinefelter syndrome (XXY): Males with extra X chromosomes (XXY) can exhibit traits usually seen in females.
• Nondisjunction: Failure of chromosomes to separate during Anaphase I or II of meiosis. Can occur in either parent (egg or sperm).

Strawberry Chromosomes

• Strawberries are octoploid (8 sets of chromosomes). If the base number is 7, a strawberry cell has 56 chromosomes (8 x 7).

Pedigree Analysis

• Recessive traits: Appear when both parents are carriers and pass down recessive traits (e.g., aa phenotype) to their offspring.
• Dominant traits: Appear in every generation.
• Genotype Deduction: Determine genotypes by analyzing inheritance patterns. Symbols like A/a can be used to deduce individual genotypes based on phenotypes.

DNA Structure

• DNA structure includes phosphate groups, deoxyribose sugars, and nitrogenous bases (A, T, G, C).
• A nucleotide consists of one phosphate, one sugar, and one nitrogenous base.
• DNA strands are antiparallel (one strand 5' to 3', the other 3' to 5') with complementary base pairing (A-T, G-C).

Pedigree Genotype Deduction

• Analyzing inheritance patterns to determine possible genotypes.
• Use symbols to deduce genotypes based on an individual's phenotype and family history. For instance, unaffected individuals might be homozygous dominant (AA) or heterozygous (Aa) for a recessive trait.

This quiz covers fundamental concepts in genetics, including chromosome numbers in different species, the nature of gametes, and key genetic terms like homozygous and heterozygous. Dive into the world of inheritance, mutations, and reproductive biology.