Genetics Chapter 8 Review

Genetics Overview

• Offspring resemble their parents, but not exactly.

• Siblings bear similarities yet are not genetically identical.

The Human Life Cycle

• Adults produce gametes in their gonads through meiosis.

• Fertilization: Sperm cells fertilize egg cells to form zygotes.

• Embryo Development: Repeated cell divisions lead to the formation of an embryo, which grows into a fetus. After birth, continued growth leads to adulthood.

/

Chromosomes and Genes in Humans

• Humans have 23 pairs (46) of chromosomes.

• Genes: Segments of DNA coding for proteins, analogous to words in an instruction manual.

  • Chromosomes are like pages; each contains thousands of genes.

  • Different cell types utilize genes in varying orders.

DNA Mutations and Alleles

• Mutations in DNA replication produce different gene versions (alleles).

  • Effects of mutations: detrimental, neutral, or beneficial.

• Each cell contains two copies of genes: one from the mother and one from the father (23 pairs of homologous chromosomes).

Meiosis and Genetic Variation

• Meiosis occurs in gonads (e.g., testis) to produce gametes (sperm cells).

• Zygote Formation: Diploid (2n) condition arises when a haploid (n) sperm fertilizes a haploid egg.

• Segregation: One chromosome from each homologous pair goes into a gamete.

• Independent Assortment: Random arrangement during metaphase I leads to diverse genetic combinations (about 8 million combinations for humans).

• Genetic diversity results from fertilization (64 trillion possibilities).

Gregor Mendel and Principles of Inheritance

• Gregor Mendel: Foundational figure for understanding inheritance rules using pea plants.

• Mendelian principles apply to various human genetic diseases.

Genetic Terminology

• Phenotype: Physical traits of an individual, influenced by genotype.

• Genotype: Genetic makeup describing alleles for a specific gene.

• Homozygous: Identical alleles for a gene.

• Heterozygous: Different alleles for a gene.

• Dominant Alleles: Expressed in both homozygous and heterozygous conditions.

• Recessive Alleles: Expressed only in homozygous conditions.

Genetic Diseases in Humans

• Cystic Fibrosis: Recurring lung infections, recessive disease; heterozygotes (carriers) show no symptoms.

• Huntington's Disease: Dominant genetic disorder; symptoms appear in middle age and are fatal.

Punnett Squares in Genetics

• Punnett Square: A tool to predict outcomes of genetic crosses (e.g., cystic fibrosis carriers).

• Example Cross: Ff x Ff (F = normal allele, f = recessive allele).

Dihybrid Crosses

• Involve two traits; determine possible gametes and predict phenotypic ratios (e.g., 9:3:3:1).

Extensions of Mendelian Genetics

• Incomplete Dominance: Heterozygotes display an intermediate phenotype (e.g., red vs. pink flowers).

• Codominance: Both alleles expressed simultaneously (e.g., ABO blood type).

• Multiple Alleles: ABO blood group has three alleles (IA, IB, i) with IA and IB being codominant.

Sex Determination and Linkage

• Humans possess 23 pairs of chromosomes: 22 autosomes and one pair of sex chromosomes (XX in females, XY in males).

• Sex-linked Genes: Associated with sex chromosomes; inherited patterns differ between genders.

Hemophilia and Recessive X-Linked Traits

• An example of a recessive X-linked trait; more prevalent in males due to single X chromosome.

Pedigrees and Genetic Counseling

• Pedigree: Chart illustrating the inheritance of traits through generations using symbols (circles for females, squares for males).

• Analyze pedigrees to determine modes of inheritance for genetic conditions.