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
Jacob Syndrome Results (3)
- Men
- tall but mostly normal testosterone production & development.
- May have increased risk of learning disabilities, ADHD, depression, anxiety and autism spectrum disorder.
Klinefelter Syndrome Chromosome
XXY
Klinefelter Syndrome Results (5)
- Men
- tall and infertile.
- Small testes, produce low levels of testosterone.
4, May have mild mental impairment - May also develop enlarged breasts due to extra X chromosome
Trisomy-X or Triple X Syndrome Chromosome
XXX
Trisomy-X or Triple X Syndrome Results (3)
- Women
- may be taller than normal but no unusual physical features.
- May have increased risk of learning and intellectual disabilities
Turner Syndrome Chromosome
XO
Turner Syndrome Results (3)
- Women – short stature with altered body form.
- Many don’t undergo puberty and are infertile as ovaries don’t develop completely.
- Heart defects may lead to shorter lifespan
Deletions
- Piece of chromosome breaks off and is lost
- Lethal to eggs and sperm because they can’t do without chromosomes
- Possible for live birth to occur (but rare)
Cri-du-chat (cat cry)
Results from a deletion of chromosome #5
Translocations
- Piece of chromosome breaks off and re-attaches to a new location
Attaches either on same chromosome or on another one - Results in subtle changes in gene expression and function
- Increased risk of cancers and chronic myelogenous leukemia
Recessive Genetic Disorders Disease is expressed if:
Person inherits TWO defective alleles (one from each parent)
Recessive Disease can be inherited but not _________ when _____ allele is received, making it more common in _______ population than dominant disease causing alleles.
- expressed
- one
- general
examples of recessive genetic disorders (3)
- Phenylketonuria (PKU)
- Tay Sach’s
- Cystic Fibrosis
Phenylketonuria (PKU)
- Mutation of chromosome #1
- Accumulation of phenylalanine due to a missing enzyme required to metabolize it
- Phenylalanine is converted to phenylpyruvic acid instead (toxic at high concentrations)
- Guthrie test (PKU test done at birth) is used to determine if child is affected with this disorder
Tay-Sachs Disease
- Chromosome #15 affected
- Enzyme deficiency disease
- Unable to metabolize a special lipid causing it to accumulate in the brain leading to cerebral degeneration
- Very common in Ashkenazi Jewish population
Cystic Fibrosis
- Found on chromosome #7
- Defective version of protein that normally aids in transportation of chloride across cell membrane of epithelial cells
- Cells produce thick, sticky mucous that clogs the lungs and pancreas
Dominant Genetic Disorders (3)
- Follows same pattern of expression as other dominant traits
- Only one allele is required for disease to occur
- Are uncommon because they tend to eliminate themselves from the population
Huntington Disease
- Progressive nerve degeneration leading to physical and mental disability and death
- No known cure and is known as a dominant-lethal allele
- Genetic testing is available to determine if an individual has the dominant allele causing Huntington’s
