Chapter 29 Hereditary Flashcards
(44 cards)
1
Q
genetics
A
- study of the mechanism of hereditary
- basic principles of genetics were proposed in mid-1800s by Mendel, who studied inherited characteristics that were either all or none
- human traits are much more complex than that
2
Q
Human Genome Project (1990-2003)
A
- has determined human DNA sequence, which can aid in genetic research and genetic screening
- cost 3 billion dollar
3
Q
genetics introduction
A
- development of a new individual is guided by the gene-bearing chromosomes it receives from its parents
- diploid number of chromosomes:
- diploid number = 46 (23 pairs of homologous chromosomes) = 2n
- in all cells except gametes (egg or sperm)
- haploid number = 1n
4
Q
chromosomes
A
- homologous chromosomes are pairs of chromosomes -> one set from egg and one from sperm
- 1 pair of sex chromosomes determines the genetic sex ( XX - female, XY - male)
- 22 pairs of autosomes guide expression of most other traits
5
Q
gene pairs (alleles)
A
-alleles are genes that occur at same locus (location) on homologous chromosomes
6
Q
homozygous
A
alleles controlling a single trait are the same
- TT
- tt
7
Q
heterozygous
A
- alleles for a trait are different
- Tt
8
Q
dominant
A
-an allele that masks or suppresses its (recessive) partner
9
Q
Gregor Mendel
A
- austrian monk
- 1822
- teacher, in charge of monastery garden
- two types of pea plants- tall and short
- self pollinating vs cross pollination
- cross pollinating a tall and short plant produces all tall plants, but next generation will produce 3 tall and 1 short (25%)
10
Q
karyotype
A
-diploid chromosomal complement displayed in homologous pairs
11
Q
genotype
A
-the genetic makeup (Tt)
12
Q
phenotype
A
-the way the genotype is expressed (tall pea plant)
13
Q
sexual sources of genetic variation
A
- chromosomes segregation and independent assortment
- crossover of homologous
- random fertilization of eggs by sperm
14
Q
segregation and independent assortment
A
- independent assortment- during gametogenesis, maternal and paternal chromosomes are randomly distributed to daughter cells, occurs during metaphase of meiosis
- segregation- distribution of 2 alleles for a trait to different gametes during meiosis
- the number of gamete types = 2^n, where n is the number of homologous pairs
- ex. in a mans testes, 2^n = 2^23 = 8.5 million
15
Q
crossover and genetic recombination
A
- genes on the same chromosome are linked
- chromosomes can cross over; forming a chiasma, and exchange segments
- crossover occurs during prophase of meiosis
- recombinant chromosomes have mixed contribution from each parent
- homologous chromosomes synapse during prophase of meiosis 1
- each chromosome consists of two sister chromatids
- one chromatid segment exchanges positions with a homologous chromatid segment- AKA- crossing over occurs forming a chiasma
- the chromatids forming the chiasma break, and the broken off ends join their corresponding homologues
- at conclusion of meiosis, each haploid gamete has one of the 4 chromosomes -> two of the chromosomes are recombinant (they carry new combinations of genes)
16
Q
random fertilization
A
- random fertilization adds to a genetic variation because any sperm can fuse with any ovum (unfertilized egg)
- 70 trillion diploid combinations- not counting crossing over!
17
Q
types of inheritance
A
- most traits are determined by multiple alleles or by the interaction of several gene pairs:
- dominant-recessive inheritance
- multiple allele inheritance
- polygene inheritance
18
Q
dominant-recessive inheritance: punnett square
A
- reflects the interaction of dominant and recessive alleles
- punnett square- predicts the possible gene combinations resulting from the mating of parents of known genotypes
- ex. probability of genotypes from mating two heterozygous parents (Tt)
- T- tongue roller and t- cannot roll tongue
- TT and tt are homozygous; Tt is heterozygous
- creates- TT, tt, Tt, Tt
19
Q
simple dominant recessive inheritance
A
- A) attach earlobes (unattached-dominant)
- B) roll tongue
- C) dimples
- D) freckles
- E) curly hair
- F) cleft chin
- G) widows peak
- H) hand crossing (left on top is dominant)
20
Q
dominant disorders
A
- uncommon because many are lethal and result in death before reproductive age
- EXCEPTION- huntingtons disease- caused by a delayed action gene- person survives long enough to reproduce
21
Q
dominant-recessive inheritance
A
- most genetic disorders are inherited as simple recessive traits
- albinism, cystic fibrosis, and Tay-Sachs disease
- heterozygotes are carries who do not express the trait but can pass it on to their offspring
22
Q
The ______ is an individuals outward appearance while the ______ is an individual genetic makeup
A
- phenotype; genotype*
- genotype; phenotype
- allele; gene
- gene; allele
23
Q
a person whose genetic makeup includes the gene pair bb is _____
A
- codominant
- heterozygous
- homozygous dominant
- homozygous recessive*
24
Q
incomplete dominance
A
- heterozygous individuals have an intermediate phenotype
- ex. sickling gene
- SS= normal Hb is made
- Ss= sickle cell trait (both aberrant and normal Hb are made); can suffer a sickle cell crisis under prolonged reduction in blood O2
- ss= sickle cell anemia (only aberrant Hb is made; more susceptible to sick-cell crisis
25
multiple allele inheritance
- genes that exhibit more than two allele forms
- ABO blood grouping is an example
- three alleles (I^A, I^B, i) determine the ABO blood type in humans
- I^A and I^B are codominant (both are expressed if present), and i is recessive
26
sex-linked inheritance
- inherited traits determined by genes on the sex chromosomes
- X chromosomes bear over 1400 genes (many for brain function); Y chromosomes carry about 200 genes
- more than 100 sex-linked disorders have been mapped to the X chromosomes
- X-linked genes are found only on the X chromosome, and are typically passed from mothers (carriers) to sons (e.g. hemophilia or red-green color blindness)
- daughters remain unaffected or carrier
- this is because daughter take both XX and the dominant will remain dominant...if the son inherits only the carrier X it will present itself
- males have just one X chromosome, thus all X-linked alleles are expressed in males, even if recessive
27
why are most calico cats female
- coat color is determined by X chromosome
- one X has allele for black spots
- one X has allele for orange spots
- female cats can have a combination of black and orange spots, males (only one X) can have only one color
28
polygene inheritance
- depends on several different gene pairs at different locations acting in tandem
- results in continuous phenotypic variation between two extremes
- ex. skin color, eye color, height, metabolic rate, intelligence
- skin color is controlled by 3 separately inherited genes, each existing in 2 allelic forms: A, a; B, b; C, c
- the A, B and C alleles confer dark skin pigment and their effects are additive
- when heterozygous individuals mate, a broad range of pigments is possible
29
chromosomal disorders
- if two copies of an autosomal chromosome fail to separate during meiosis, an individual may be born with 3 copies of a chromosome
- down syndrome- 3 copies of chromosomes 21
30
genotype vs phenotype
-genotype (excluding mutations) is unchanging (rock) while phenotype can be molded or changed (clay)
31
phenocopies
- environmentally produced phenotypes that mimic conditions caused by genetic mutation during embryonic development
- thalidomide babies- medications affected the babies in utero
32
environmental factors
- can influence genetic expression after birth
- poor nutrition can affect brain growth, body development, and height
- childhood hormonal deficits can lead to abnormal skeletal growth and proportions
- getting a tan
33
what is an example of a disease caused by a lethal dominant gene
- tay-sachs disease
- huntingtons disease*
- cystic fibrosis
- sickle cell anemia
34
what is the probability of a mother who has a genotype I^A I^B and a father who has a blood type O having a child who has blood type O
- 0%*
- 25%
- 50%
- 100%
35
beyond DNA: regulation of gene expression
- 3 levels of controls are found in human genome
- first layer- protein coding genes -> involve less than 2% of a cells DNA
- DNA that is a blueprint for protein synthesis
- secondar layer- small RNA -> found in non-protein-coding DNA
- third layer- epigenetic marks -> stored in proteins and chemical groups that bind to DNA and in a way chromatin packaged
36
small RNAs
- microRNAs (miRNAs) and short interfering RNAs (siRNAs)
- act directly on DNA, other RNAs, or proteins
- may silence genes or prevent their expression and appear to play a role in directing apoptosis during development
- in future, RNA interfering drugs may treat disease such as age-related macular degeneration and parkinsons disease
37
epigenetic marks
- information stored in the proteins and chemical groups bound to DNA
- determine whether DNA is available for transcription or silenced
- if DNA is like the alphabet than epigenetic marks are like punctuation
- epigenetics= study of heritable changes in gene expression -> change in phenotype without change in genotype
- lifestyle can affect individual epigenetics: pollution and diet
38
extranuclear (mitochondrial) inheritance
- not all DNA Is located in cells nucleus
- mitochondrial contain 37 of their own genes, referred to as mitochondrial DNA (mtDNA)
- mitochondria are transmitted to embryo by mother in cytoplasm of egg
- errors in mtDNA are linked to rare disorders
- usually problems associated with oxidative phosphorylation (cellular respiration)
- some muscle and neurological problems, possibly Alzheimer's and parkinsons disease
39
genetic screening, counseling, and therapy
- newborn infants are routinely screened for a number of genetic disorders: congenital hip dysplasia, imperforate anus, and other metabolic disorders
- other examples:
- screening adult children of parents with huntingtons disease
- testing a women pregnant for the first time after age 35 to see if the baby has trisomy-21 (down syndrome)
40
carrier recognition
- two major avenues for identifying carriers of gene: pedigrees and blood tests
- pedigrees trace a particular genetic trait through several generation; helps to predict the future
- blood test and DNA probes can detect the presence of unexpressed recessive genes
- tay-sachs and cystic fibrosis genes can be identified by such tests
41
fetal testing
- used when there is known risk for a genetic disorder
- amniocentesis- amniotic fluid is withdrawn after the 14th week and fluid and cells are examined for genetic abnormalities
- chorionic villus sampling (CVS): chorionic villi are sampled and karyotyped for genetic abnormalities
42
human gene therapy
- genetic engineering has the potential to replace a defective gene
- defective cells can be infected with a genetically engineered virus containing a functional gene (because they can enter the nucleus)
- the patients cells can be directly injected with "corrected" DNA
43
ethical issues in human genetics
- if human cells can be manipulated to cure diseases, they can also be manipulated to produce certain traits:
- height, eye color, sex, appearance, intelligance
- should we gain the opportunity to design our bodes? human cloning?
44
a color blind man marries a women with normal vision. the womans father was also color blind. what is the chance that their first child will be a color blind son
- 0%
- 25%*
- 50%
- 100%
