Unit 11 Flashcards
Heredity
the delivery of traits from parent to offspring
Genetics
the scientific study of heredity
blending hypothesis
inherited traits are determined from the blending together of material from parents
How did Mendel discover the basic principles of heredity?
Mendel cross-fertilized pea plants
Cross-fertilization
fertilization of one plant from pollen of ANOTHER plant
True Breeding Plant
plant that only produces offspring with the same traits when it self-fertilizes
What was Mendel’s argument about his results? (2)
1) A unit of heredity can exist in more than 1 form
2) An organism inherits two units of heredity (alleles), one from each parent
Alleles
alternate versions of a gene
Dominant Allele
allele that is fully expressed in the organism’s appearance
Recessive Allele
allele that only influences the organism’s appearance when the dominant allele is not present
Homozygous
an organism having a pair of identical alleles for a character
Heterozygous
an organism that has two different alleles for a gene
Phenotype
an organism’s traits (what you see)
Genotype
an organism’s genetic makeup (combination of alleles)
The Law of Segregation
Two alleles separate during meiosis so that each gamete contains only one allele for each gene
The Law of Dominance (2)
- if an organism has two alleles, the dominant allele will determine the trait
- the unexpressed allele is recessive
Punnett Square
diagram used to determine the expected ratio of genotypes and phenotypes in the offspring of parents with known genotypes
Testcross
a mating between an individual of dominant phenotype and unknown genotype and a homozygous recessive organism
How do you analyze testcross results? (2)
- If all offspring have dominant phenotype, then the parent is homozygous dominant
- If half offspring have dominant phenotype and half have recessive, then the parent is heterozygous
Dihybrid Cross
the crossing of parental varieties differing in two characteristics
What are possible outcomes of a dihybrid cross? (2)
- dependent assortment
- independent assortment
Dependent Assortment
traits are transmitted as a package
Independent Assortment
traits are transmitted independently
Law of Independent Assortment
the inheritance of one trait has no effect on the inheritance of another
Unlinked Alleles
alleles located on different chromosomes
What can unlinked alleles do?
move independently during meiosis and get sorted into gametes independently
What is a family pedigree? (2)
- Shows the history of a trait in a family
- Allows geneticists to analyze how human traits are inherited
How many symbols are used in family pedigrees?
2
What are the symbols for male and female on a pedigree?
- circle for female
- square for male
What indicates that an individual has a disease on a family pedigree?
the square or circle is shaded
What does a horizontal line signify on a family pedigree?
the parents having children
What does a vertical line signify on a family pedigree?
children
What do overhead connections signify?
siblings
Wild-type Traits
those seen most often in nature (not necessarily dominant!)
How are genetic disorders caused?
mutated/changed alleles that alter protein function
What does the loss of normal protein function cause?
symptoms of disorders through hypo/hyper activity
Autosomal Disorders
mutated genes are on autosomes (not sex chromosomes)
Sex-Linked Disorders
disorders-mutated gene is on a sex chromosome
Dominant Disorders
caused by mutated dominant allele
Recessive Disorders (2)
- caused by mutated recessive allele
- more common
How can autosomal recessive disorders appear? (2)
- Homozygous recessive individuals have the disorder
- Heterozygous individuals are carriers with “normal” phenotype
Carrier
heterozygous individual who appears normal but carries a recessive disease-causing allele
What is an example of an autosomal recessive disorder?
cystic fibrosis
What is cystic fibrosis?
it causes chronic lungs disease
What happens with cystic fibrosis as a result of the defective gene? (3)
- thick, sticky mucus that clogs the lungs
- malabsorption
- malnutrition
How can autosomal dominant disorders appear?(2)
- Heterozygous & homozygous dominant individuals have dominant disorders
- Only one dominant allele is needed to develop symptoms
What is an example of an autosomal dominant disorder?
Huntington’s disease
What is Huntington’s disease?
a neurodegenerative disorder
What does the Huntington’s disease protein cause?
- protein aggregates in brain cells
- death
What is a side effect of Huntington’s disease?
involuntary movement
Genetic Test
test that can detect the presence of disease-causing alleles
What are genetic tests that can be done? (2)
- amniocentesis
- chronic villus sampling
What are some patterns that cannot be explained by Mendel’s laws? (5)
1) multiple alleles
2) codominance
3) polygenic traits
4) pleiotropy
5) environmental factors
How many alleles are there for the human ABO gene?
3
How is the A gene represented?
I^A
How is the B gene represented?
I^B
How is the O gene represented?
i
What are the possible genotypes for A? (2)
I^AI^A and I^Ai
What are the possible genotypes for B? (2)
I^BI^B and I^Bi
What is the possible genotype for O
ii
What is the possible genotype for AB?
I^AI^B
What blood type is the universal donor?
O negative
Codominance (2)
- both alleles in the genes pair of a heterozygote are fully expressed
- no dominant or recessive allele
What is an example of codominant alleles?
I^A and I^B
Polygenic Traits (2)
- exhibit continuous variation
- many genes control a single trait
Continuous Variation
phenotypes display a continuous spectrum in the population, not either or
What are examples of continuous variation? (2)
- skin color
- height
How is continuous variation created?
combining the effects of alleles from multiple genes
Pleiotropy
when a single gene controls or influences multiple metabolic pathways and has multiple phenotypic effects
What disease is an example of pleiotropy?
cystic fibrosis
Environmental Factors
The environment can increase the variation in a trait
What are some examples of traits that are controlled by environmental factors? (2)
- human height
- freckling in humans
What are environmental factors that can influence human height? (2)
- diet
- health
What is an environmental factor that can influence freckling?
the amount of sunlight and its intensity
Biological Sex Determination (4)
- Human somatic cells have 22 pairs of autosomes and 1 pair of sex chromosomes (genes that determine biological sex)
- Females are XX
- Males are XY
- chances of conceiving a male or female child (assigned at birth) are equal
Sex-linked traits (3)
- Most sex-linked traits are located on the x chromosome
- A much smaller number of sex-linked traits are found on the Y-chromosome
- Sex-linked traits can be recessive or dominant
X-linked recessive traits in males (3)
- Males only need 1 recessive allele to have the trait
-A man with hemophilia is XhY - Men are more likely to have recessive X-linked traits because they only have one chance (one X chromosome) to get the healthy allele
X-linked recessive traits in females (3)
- Females need 2 recessive alleles to have the trait
-A woman with hemophilia is XhXh
-A woman who is a carrier is XHXh
What are two examples of X-linked recessive disorders?
- Color blindness
- Hemophilia
What is Hemophilia? (3)
- An x-linked recessive disorder where protein used for blood clotting is not produced
- Clotting factor proteins are needed to stop bleeding following injury
- Small injuries can cause excessive bleeding and death
What is the inheritance of Hemophilia? (3)
- A man with hemophilia is XhY
- A woman with hemophilia is XhXh
- A woman who is a carrier is XHXh
What is an X-linked dominant trait? (3)
- Refers to situations where a single dominant allele on the X chromosome can lead to a trait/condition
- Extremely rare
- Affected fathers pass the trait to ALL of their daughters in pedigrees
What is an example of an X-linked dominant trait? (3)
- X-linked rickets (bone lesions)
- A man with X-linked rickets is XHY
- A woman with X-linked rickets is XHXh or XHXH
What is independent assortment? (2)
- When the inheritance of one trait has no effect on the inheritance of another
- Genes on separate chromosomes move through meiosis independently
Linked Genes (3)
- are located on the same chromosome
- move together through meiosis and fertilization
- are inherited together unless uncoupled by crossing over
What is a linkage group?
Genes located on the same chromosome
Unlinked Genes
Located on different chromosomes
How does crossing over unlink genes? (2)
- The further apart alleles are on a chromosome, the more likely crossing over will separate them and they will be inherited as though they are not linked
- Linked alleles located closely on a chromosome are less likely to be separated by crossing over
Who was TH Morgan? (2)
- The first to propose the linkage of genes and that characteristics are inherited together
- When mating fruit flies, his observed offspring ratios that were different from what he predicted assuming independent assortment
Key proposals made by TH Morgan (2)
- Alleles for linked traits are on a shared chromosome and don’t independently assort
- Linked alleles could be uncoupled via crossing over (recombination) to create alternative phenotypic combinations, but these new phenotypes would occur at a much lower frequency
What is a parental offspring?
Same phenotype as one of the parents
What is a recombinant offspring?
Phenotypes differ from either parent
What is recombinant frequency? (2)
- The percentage of recombinant offspring among the total
- Calculated by dividing # of recombinants by total offspring and multiplying by 100
Why do ‘unlinked’ recombinant phenotypes occur less frequently than the ‘linked’ parental phenotypes?
Because crossing over is a random process
