Human Genetics Study Notes

Human Karyotype

• Humans have a total of 23 pairs of chromosomes.
  • 22 pairs are normal autosomes (non-sex chromosomes).
  • 1 pair consists of sex-determining chromosomes (XX for females, XY for males).

Karyotype Definition

• A karyotype is a visual representation of chromosomes organized by size and shape, arranged from biggest to smallest.

Homologous Chromosomes

• Recognized by size and shape.
  • Example: Homologous chromosomes are similar in length and gene position, even though they may carry different alleles.

Chromosome Functions

• The sex-determining chromosomes dictate the development of sexual characteristics in a fetus.
  • Y chromosome: Triggers the development of male characteristics (e.g., penis, testes).
  • X chromosome: Carries various genes affecting traits beyond sex.

Genetic Mutations on Y Chromosome

• A mutation on the Y chromosome can lead to differences in sexual development despite still being XY.
  • Example: A single base nucleotide change can result in atypical genital formation (testes in place of ovaries).

Gender and DNA

• Women have two X chromosomes (XX), leading to a greater amount of DNA and genetic information compared to males (XY) which could hint at 'superiority' in terms of genetic diversity.
• Men's traits, particularly related to aggression and other physical characteristics, may often be influenced by these chromosomes alongside environmental factors.

Quantitative Traits

• Traits like height and gender expression are polygenic and influenced by multiple genes, leading to a bell-shaped distribution.
• Variation occurs along a spectrum, reflecting a range of expressions for both males and females.

Chromosomal Diseases and Gender

• Males are more susceptible to sex-linked genetic disorders (e.g., hemophilia, color blindness) because they possess only one X chromosome.
• Mutations on the X chromosome often manifest as diseases more frequently in males.

Pedigree Charts

• Used to track inheritance of traits in families.
• Sex-linked traits affected more frequently in males than females provide informative patterns in these charts.

Understanding Genetic Conditions

• Hemophilia example:
  • Carrier mother: X^H X^h (normal and hemophilia alleles).
  • Male inheritance: X^H Y would indicate normal male; X^h Y indicates a hemophiliac male.
  • Resulting Punnett square shows a higher probability of males being affected by sex-linked traits.

Autosomal vs. Sex-Linked Traits

• Autosomal Dominant traits appear in every generation regardless of gender.
• Autosomal Recessive traits may skip generations as carriers (heterozygous) can pass the gene without expressing it.
  • Example: Cystic fibrosis may appear if both carriers reproduce.

Genetic Counseling and Family History

• Genetic conditions prompt the tracking of family histories to ascertain health risks.
• Tools such as pedigree charts can assist in visualizing inheritance patterns.

Modern Genetic Solutions

• Advances in genomic sequencing allow early detection of predispositions to genetic disorders.
• Ethical considerations arise regarding privacy and risk of discrimination based on genetic information.