LEC 18 Flashcards
Sex Linked Inheritance
X & Y Chromosomes DIFFERENCES
- Size and shape
- Centromere location
- How they function in the body
- Carry different genes which code for different proteins
X & Y Chromosomes are not ____________ to each other
- homologous
X-Chromosome (5)
- Has approx. 1000 genes to code for various proteins
- Includes the genes needed to be “female”
- Also codes for other traits and characteristics not specifically related to being female
- Females have a pair of homologous X chromosomes (XX)
- Have a “back-up” so if something is wrong with one, the other can still function normally
Y-Chromosome (4)
- Y-chromosome has only a few genes
- Includes the genes needed to be “male” (development of male genitalia, sperm and testosterone production)
- Males have a non-homologous pair of sex chromosomes (XY)
- Don’t have a “backup copy” and therefore is a greater chance of inheriting diseases associated with mutations of the sex chromosomes
Sex Linked Inheritance
Inheritance patterns that depend on genes located on sex chromosomes
Sex Linked Inheritance Y-linked
- gene found on the Y chromosome
- Relatively few documented examples (Y-linked infertility) because sole purpose is to produce male traits in offspring
Sex Linked Inheritance X-linked
- gene found on the X chromosome
- Many examples because it carries information not related to determining gender of offspring
X-Linked Inheritance in FEMALES
- behaves like inheritance of recessive autosomes traits with homologous pairs of genes
- Individual needs two (2) of the affected genes for trait/disorder to be expressed
X-Linked Inheritance in MALES
- genotype & phenotype are determined solely by the X chromosome
- Individual needs only one (1) affected gene (from mom) for trait/disorder to be expressed
Hemophilia (3)
- Best known example of X-linked inheritance
- “bleeder’s disease”
- Affected individuals lack a blood clotting factor
X-Linked Inheritance: Males receive trait from their carrier _________
mothers
X-Linked Inheritance: Females _________ affected but are often carriers. Carriers are ___________.
- rarely
- heterozygous
X-Linked Inheritance: Affected fathers _________ pass the trait to their sons
cannot
X-Linked Inheritance: Affected _____ will pass the affected gene to their daughters.
- Daughter will either become a ______ or have the disorder
- Depends on the _______ they receive from their ________
- fathers
- carrier
- gene
- mother
Sex influenced traits
Some traits influenced by the sex of the individual
Sex influenced traits : baldness
Chromosome Abnormalities can happen during: (3)
DNA Replication
Mitosis
Meiosis
In mitosis and meiosis, abnormalities can result in the daughter cells having the _______ number of chromosomes
wrong
Several different mechanisms can alter the number of chromosomes in daughter cells: (3)
- Nondisjunction
- Deletions
- Translocations
Nondisjunction (2)
- Failure of homologous chromosomes or sister chromatids to separate properly during cell division
- Results in too many/not enough chromosomes in an autosome or gamete
Mitosis Results of Nondisjunction (2)
- Both sister chromatids go to one cell
- Don’t see results of nondisjunction in mitosis as daughter cells usually die off
Meiosis Results of Nondisjunction (4)
- Homologous chromosomes/sister chromatids fail to separate resulting in too many copies in egg or sperm 2. More serious as the affected gametes have the potential to become an entire organism
- Most are unlikely to survive and die in early embryonic development
- Some cases result in live births
Nondisjunction in Meiosis: Down Syndrome
AKA “Trisomy 21”
- Three copies of chromosome #21 are present
- Incidence arises with advancing age of mother
- May also originate with father if both parents are over 35
Jacob Syndrome Chromosome
XYY