Unit 5 Flashcards
Monosomy
(2n-1) occurs when an organism has one of the two chromosomes in a homologous pair
Trisomy
(2n+1) occurs when an individual has three instead of two chromosomes in a homologous pair, only three trisomy are viable beyond birth.
What are the three reasons that nondisjunction can happen?
- Early anaphase- chromosome spindle fibers start pulling before the official trigger 2. Spindle fiber attachment damages the chromosome 3. Synaptonemal complexes could fail to dissolve- the glue that holds homologous chromosomes together doesn’t let go.
Law of Dominance
only one form of the trait will appear in the next generation; if an organism inherits at least one dominant allele, it will exhibit the dominant phenotype; if an organism has 2 recessive alleles, they will show the recessive phenotype.
Law of Segregation
each organism has two factors for each trait; factors separate during meiosis; each gamete contains only one of the factors; increases genetic variation.
Law of Independent Assortment
each factor segregates independently from other factors
FOIL AaBb
AB, Ab, aB, ab
Yay free card ᕙ(ಠਊಠ)ᕗ
Dihybrid Cross Example
in a cross between AaBb X AaBb, what is the probability of having an offspring of aabb? Aa X Aa (¼ probability) Bb X Bb (¼ probability) ¼ X ¼ = 1/16 (use punnet square to find probabilities)
Genetic Recombination
the closer two genes are together, the more likely they will be inherited together; the farther apart two genes are, the more likely they will be recombined.
Recombinant DNA
genes where crossing over has occurred between them.
Multiple Alleles in Blood Types
IA= A antigen allele, IB= B antigen allele, i= neither antigen allele.
Sex Linked Definition
any gene that is located on a sex chromosome (XX or XY); in humans, most sex-linked genes are found on the X chromosome
Sex Linked Disorders
males only need one copy of a sex linked disorder to produce the affected phenotype because they only have one of each chromosome; females need 2 X chromosomes with the disorder to produce the phenotype
Y-Linked Disorders
always passed from father to son; only males have this disease; rare because there are less genes on a y chromosome; 100% chance that guys will inherit the disease if their father has it, like ear hair
Polygenic Inheritance
several genes contribute to a single phenotype; example eye color and height; wide variety of phenotypes; most human genetics are polygenic
Incomplete Penetrance
an individual may have the genotype, but won’t produce the phenotype; BRCA1 gene when mutated causes cancer, but only 80% of people with the gene will develop breast cancer. Polydactyl is an autosomal dominant gene that causes extra fingers or toes, mot all individuals that inherit the gene will show the condition
Pleiotropy
occurs when a single mutant gene affects two or more distinct and seemingly unrelated traits.
Epistasis
interaction of two or more gene pairs at different loci influence the same trait, but one allele has an overriding effect on the phenotype; gene A controls gene B
Pedigree
family tree that records and traces the occurrences of a trait
Autosomal Recessive Disorders
individual needs both recessive genes to have the disorder; aa only; rare in populations; parents are usually heterozygous; skips generations; equal ratios in males and females; gene found on chromosomes 1-22; parents must be heterozygous to have an affected child
Autosomal Dominant Disorders
only needs one of the 2 alleles to have the disorder; AA or Aa; doesn’t skip generations; very rare; gene is found on chromosomes 1-22; parents must be heterozygous to have an unaffected child
X-Linked Dominant
sex linkage cannot be confirmed; 100% incidence of affected daughters from an affected father suggests X-linked dominant.
X-Linked Recessive
sex linkage cannot be confirmed; 100% incidence of affected sons from an affected mother suggests x-linked recessive.
Environmental Effects on Genetics
environmental factors influence gene expression and can lead to phenotypic plasticity(individuals with the same genotype exhibit different phenotypes in different environments)
Explain how meiosis results in the transmission of chromosomes from one generation to the next.
Meiosis results in haploid gametes which are sperm or egg. When sperm fertilizes the egg it becomes a diploid zygote because now it has two pairs of DNA that were passed on during fertilization.
Describe similarities and/ or differences between the phases and outcomes of mitosis and meiosis.
Mitosis and meiosis both include the phases of prophase, metaphase, anaphase, and telophase. Mitosis includes prometaphase while meiosis doesn’t and meiosis includes crossing over and independent assortment which doesn’t happen in mitosis. Meiosis produces 4 genetically different haploid sex cell gametes, but mitosis produces two genetically identical diploid autosomal daughter cells. Both create daughter cells.
Explain how the process of meiosis generates genetic diversity
Crossing over and Independent assortment
Explain the inheritance of genes and traits as described by Mendel’s laws
The law of dominance says that only one form of the trait will appear in the next generation; if an organism inherits at least one dominant allele, it will exhibit the dominant phenotype; if an organism has 2 recessive alleles, it will show the recessive phenotype. The law of segregation says that each organism has two factors for each trait that separate during meiosis; each gamete contains only one of the factors; which increases genetic variation.
Explain deviations from Mendel’s model of the inheritance of traits.
Incomplete dominance- the traits can blend if 2 different traits combine. Codominance- one or both are expressed at the same time. Multiple Alleles- blood types where AO blood is still type A blood. X-linked- If the change is recessive, anyone with two copies of the dominant gene will be affected by the change and anyone with only one copy will just be a carrier.
Explain how the same genotype can result in multiple phenotypes under different environmental conditions.
The environmental conditions can change the phenotype depending on how often they’re in the sun, what they eat, season changes, and the temperature that they’re in even if they have the same genotype.
Explain how chromosomal inheritance generates genetic variation in sexual reproduction.
Each gamete has different genetic material and when it combines with another random gamete to form a zygote, they have a new combination of genetic information that was combined from their parents.
Haploid
half of the number of chromosomes found in diploid cells; only one set of chromosomes; 23 chromosomes
Diploid
the total number of chromosomes, which consists of two sets; 46 chromosomes
Homologous Chromosome
chromosomes that have the same length and centromere positions; the same genes in the same locations
Autosomal Chromosomes
all of the chromosomes that don’t determine the sex of an individual; humans have 22 pairs of autosomal chromosomes
Sex chromosomes
pair of sex chromosomes (gametes); XX is female XY is male
Zygote
diploid cell formed by fertilization of an egg
Genotype
refers to the alleles an individual receives at fertilization; Aa
Phenotype
physical appearance based on the genotype
Allele
Alternate forms of genes; gene for eye color, allele for brown or blue eyes
Locus
location of gene on homologous chromosomes
Pleiotropy
occurs when a single mutant gene affects two or more distinct and seemingly unrelated traits.
Homozygous
genotype with the same alleles; GG gg
Heterozygous
genotypes with different alleles; Gg
What are the phases of meiosis I?
Prophase I, Metaphase I, Anaphase I, Telophase I
What is the purpose of meiosis I?
Separating homologous chromosomes and splitting a diploid cell into two non-identical haploid cells.
How do homologous chromosomes separate during anaphase?
Homologous chromosomes are pulled apart by the spindle fibers, but sister chromatids stay attached
What is crossing over? When does it occur? What is the purpose of crossing over?
exchange of genetic material between non-sister chromatids of homologous chromosomes; Prophase I; Increasing Genetic Variation
What is independent assortment? When does it occur? How does it increase genetic diversity?
homologous chromosomes separate independently; random; Metaphase 1; The random order changes which sister chromatids get put in each cell
What are the phases of meiosis II?
Prophase II, Metaphase II, Anaphase II, and Telophase II
What is the purpose of meiosis II?
Separate sister chromatids and turn the 2 haploid cells into four haploid gametes
Describe the daughter cells resulting from meiosis.
Non-identical haploid gametes
Are the daughter cells resulting from meiosis diploid or haploid? How do you know? What are these cells called? Give two examples.
Haploid; there is only one set of chromosomes because they are sex-cells and gametes are haploid; Gametes; sperm and egg
Identify three differences between meiosis I and meiosis II
Meiosis I divides homologous chromosomes, crossing over occurs in prophase I, and results in 2 genetically different daughter cells. Meiosis II divides sister chromatids, crossing over does not occur, and results in 2 genetically different gametes.
Identify what part of meiosis results in the reduction of chromosome number.
Anaphase
Identify three similarities between mitosis and meiosis.
Both take place in the nuclei, involve cell division, use spindle fibers, occur in the M-phase of the cell cycle, and have the stages prophase, metaphase, anaphase, and telophase
Identify three differences between mitosis and meiosis.
Mitosis results in two genetically identical daughter cells; has one division; happens in autosomal cells. Meiosis results in four genetically different gametes; has two divisions; happens in somatic cells
What is fertilization?
two gametes combining to make a zygote
How does fertilization lead to genetic variation?
Each gamete has different DNA and when they combine to form a zygote, it makes a new combination of genes
What is the cell made immediately after fertilization called?
A zygote
What is nondisjunction? Where does nondisjunction occur in meiosis?
failure of chromosomes to separate that results in the gain or loss of chromosomes; In meiosis I or II during anaphase because the spindle fibers fail to properly separate the homologous chromosomes or sister chromatids.
Identify two genetic disorders resulting from nondisjunction.
Down syndrome, turner’s syndrome, and edward’s syndrome
What genotype(s) would a dominant trait be?
AA or Aa
What genotypes(s) would a recessive trait be?
aa
What is the probability of AaBbCCDd in a tetrahybrid cross? (assume all traits are heterozygous)
Aa- ½ Bb- ½ CC- ¼ Dd- ½ ½ X ½ X ¼ X ½ = 1/32 or 3.125%
Pedigree Key
Square= male Circle= female Half filled= carrier Filled= affected Empty= unaffected
How do environmental factors affect gene expression? Provide one example of a gene expression affected by environmental factors
They can lead to phenotypic plasticity (when individuals with the same genotype exhibit different phenotypes in different environments); Siamese cats
If a male is affected with a sex-linked trait with unaffected parents, what are the genotypes of the parents?
XAXa and XAY
What type of sex-linked cross would result in 2 normal females, 1 normal male, and 1 affected male?
XAXa X XAY
What would you look for in a pedigree to identify if the trait is dominant or recessive?
If the pedigree has carriers it is recessive, because if it was dominant, everyone with even one copy would be affected.
What would you look for in a pedigree to identify if the trait is autosomal or sex-linked?
Check to see if males and females are equally affected; if they are it’s autosomal, if one has a higher percentage than the other, it is sex-linked
Monohybrid Cross
Aa X Aa
A a
A AA Aa
a Aa aa
Dihybrid Cross
AaBb X AaBb -> AB Ab aB ab
AB Ab aB ab AB AABB AABb AaBB AaBb Ab AABb AAbb AaBb Aabb aB AaBB AaBb aaBB aaBb ab AaBb Aabb aaBb aabb
Incomplete Dominance
Can blend
CRCR= red CWCW= white CRCW=pink
CR CR CW CRCW CRCW CW CRCW CRCW
CR CW CR CRCR CRCW CW CRCW CWCW
Codominance
Both can be expressed
R= red w=white RW= red and white spots
R R W RW RW W RW RW R R R RR RR W RW RW
Multiple Alleles
Blood Types- A, B, AB, O A- AA or AO B- BB or BO AB- AB O- OO
B O A AB AO O BO OO
X-Linked
HH= normal Hh= carrier hh= affected
XH Y XH XH XH normal female XH Y normal male Xh XH Xh carrier female Xh Y affected male
