Genetics Study Guide: Unit 8

8a. Meiotic Errors and Karyotypes

Vocabulary

• Nondisjunction: Failure of chromosomes to separate properly during meiosis.
• Monosomy: Presence of only one chromosome from a pair.
• Trisomy: Presence of an extra chromosome, resulting in three copies instead of two.
• Karyotype: A visual profile of all the chromosomes in a cell.

Nondisjunction

• Occurs when chromosomes do not separate properly during cell division.

Chromosomal Conditions

• Down Syndrome: Trisomy 21.
• Edwards Syndrome: Trisomy 18.
• XXX Syndrome: Presence of an additional X chromosome in females.
• Turner Syndrome: Monosomy X, only one X chromosome.

Karyotype Information

• Can determine chromosomal abnormalities.
• Identify gender.
• Detect chromosomal disorders.

Karyotype Analysis

• Be able to identify monosomy or trisomy and determine sex from a karyotype.

8b. Mendelian Genetics and Punnett Squares

Vocabulary

• Trait: A characteristic.
• Cross: Breeding of two organisms.
• Gene: A unit of heredity.
• Locus: Location of a gene on a chromosome.
• Genotype: Genetic makeup.
• Phenotype: Physical appearance.
• Dominant allele: An allele that masks the effect of a recessive allele.
• Recessive allele: An allele that is masked by a dominant allele.
• Homozygous: Having two identical alleles for a gene.
• Heterozygous: Having two different alleles for a gene.

Father of Genetics

• Gregor Mendel: Studied pea plants.
• Laws of Inheritance:
  1. Law of Segregation
  2. Law of Independent Assortment
  3. Law of Dominance

Practice

• Determine type of inheritance from scenarios.
• Use a Punnett Square to predict genotypes, phenotypes, and probabilities.

8c. Sex-Linked Inheritance

Types of Inheritance

• Identify scenarios describing sex-linked inheritance.

Normal Sex Genotypes

• Male: XY
• Female: XX

Chromosome Differences

• X Chromosome: Larger, carries more genes.
• Y Chromosome: Smaller, carries fewer genes.

X-Linked Traits

• Recessive traits more likely in males (only one X chromosome).
• Dominant traits can be inherited by both sexes but are more apparent in females.

Punnett Squares

• Include X and Y chromosomes to describe offspring.

8d. Pedigrees

Representation in Pedigrees

• Male: Square
• Female: Circle
• Person with trait: Shaded
• Person without trait: Unshaded
• Carrier: Half-shaded

Dominant Traits

• No carriers present in the pedigree.

Sex-Linked Recessive Traits

• Males cannot be carriers.

Pedigree Analysis

• Identify individuals based on their pedigree diagram number.

Genetic Word Problems

Mendelian Genetics

Seal Whiskers

1. Cross of WW x Ww: No offspring with short whiskers.
2. Cross of WW x ww: 50% offspring with short whiskers.

Purple People Eaters

• Heterozygous (Hh) x No horns (hh): Genotype outcomes are Hh (50%) and hh (50%).
• Phenotypes include 50% with horns, 50% without.

Woodrats

• Heterozygous (Hh) x Heterozygous (Hh): Expect 75% shiny (phenotype), 25% dull.

Tongue Rolling

• Woman (Tt) x Man (tt) with first child non-roller:
  • Probability of non-roller second child: 50%.

Sex-Linked Traits

Red-Green Color Blindness

• Cross of colorblind woman (XcXc) x normal man (XY):
  • Daughters: All carriers, none colorblind.
  • Sons: 50% colorblind.

Bent Tails in Mice

• Normal female (bb) x Bent male (BY):
  • Genotype ratio: 50% Bb, 50% by.
  • Phenotype: 50% Bent tails, 50% normal tails.

Hemophilia

• Genotypes: Woman (XHXh), Man (XHY)
• Future offspring: Sons 50% non-hemophiliac, daughters 50% carriers.

These notes outline key genetic concepts, vocabulary, and problems to help prepare for Unit 8 exams.