Test #4 Review Flashcards
What is a gene?
An inherited factor (encoded in the DNA) that helps determine a characteristic.
What is an allele?
One of two or more alternative forms of a gene
What is a locus?
Specific place on a chromosome occupied by an allele
What is a genotype?
set of alleles possessed by an individual organism
What is a heterozygote?
An individual organism possessing two different alleles at a locus
What is a homozygote?
An individual organism possessing two of the same alleles at a locus
What is a phenotype or trait?
The appearance or manifestation of a characteristic
What is a characteristic or character?
An attribute or feature possessed by an organism
What is Mendles’ Monohybrid cross?
cross between two parents that differ in a single characteristic
What was Mendles’ first conclusion?
One character is encoded by two genetic factors
What was Mendles’ second conclusion?
Two genetic factors (alleles) separate when gametes are formed
What was Mendles’ third conclusion?
The concept of dominant and recessive traits
What was Mendles’ fourth conclusion?
Two alleles separate with equal probability into gametes
What is true breeding?
only 1 type of allele present
What is the principle of segregation (Mendel’s 1st law)?
Each individual diploid organism possesses two alleles for any particular characteristic. These two alleles segregate when gametes are formed, and one allele goes into each gamete.
What is the principle of independent assortment (2nd Law)?
Alleles at different loci separate independently
What is the concept of dominance?
When two different alleles are present in a genotype, only the trait encoded by one of them-the “dominant” allele - is observed in the phenotype
What is probability?
the likelihood of the occurrence of a particular event
What is used to reveal the principle of independent assortment?
dihybrid crosses
What is a pedigree?
pictorial representation of a family history; a family tree that outlines the inheritance of one or more characteristics
What is a proband?
the person from whom the pedigree is initiated
Why do male and female gametes differ in size?
The egg has all of the organelles and the sperm just carries a nucleus with DNA
What are the two sexual phenotypes?
Male and Female
What are autosomes and how many pairs do we have?
non-sex chromosomes and 22 pairs
Where are X and Y chromosome homologous?
end regions/ pseudoautosomal regions
What is the phenotype and characteristics of someone with XO?
Turner syndrome
- female traits, short, low hairline, broad chest, neck folds
What is the phenotype and characteristics of someone with XXY, XXYY, or XXXY?
Klinefelter syndrome
- Male traits, tall, small testes, reduced facial hair and pubic hair.
What is the phenotype and characteristics of someone with XXX, XXXX, or XXXXX?
Poly-X Females
- Female traits, tall and thin
What is the phenotype and characteristics of someone with XYY.
XYY Males
- male traits, tall
What is the role of the X chromosome?
The X chromosome contains genetic information essential for both sexes; at least one copy of an X is required.
What arrangement of chromosomes determines male or female?
XX- female
XY- male
- absence of Y results in a female phenotype
- one X chromosome is required for development
What is the SRY?
(Sex determining region of the Y chromosome)
How can there be a XY female?
This can happen if there is a mutation on the SRY gene on the Y chromosome and testosterone production never occurs.
How can there be a XX male?
This can occur if a X chromosome contains the SRY gene.
What does the formation of reproductive structure depend on?
- gene action
- gene and cell interaction within the embryo
- interactions with other embryos in the uterus
- interactions with the maternal environment
What are the three levels of sexual determination?
- chromosomal sex
- gonadal sex
- phenotypic sex
When is the embryo neither male nor female?
First 7-8 weeks, two undifferentiated gonads
What can alternative pathways in gene expression cause?
intermediates
When does sexual differentiation begin?
week 8
What does the SRY gene do?
- sex determining region of the Y chromosome
- encodes a transcription factor
- transcription factors turn on many other genes
- starts testosterone production
What are the two hormones that affect male pattern development?
testosterone and MIH
What is testosterone?
- steroid hormone produced by the testis
- male sex hormone
- maintains development of Wolffian duct system
What does MIH do?
Mullerian Inhibiting Hormone
- hormone produced by developing testis that causes breakdown of Mullerian (female) ducts in the embryo
What are the requirements and characteristics of female development?
- Requires the absence of the Y chromosome
- Embryonic gonad develops as an ovary
- In the absence of testosterone, the Wolffian duct system degenerates
- In the absence of MIH, the Müllerian duct system forms female reproductive system
What is androgen insensitivity?
A mutation in the androgen receptor gene (AR) causes XY males to become phenotypic females
- testosterone is produced, but no testosterone receptors so cells develop as female
What are characteristic of Androgen Insensitivity?
- No testosterone receptor, but MIH still made and degrades female reproductive system
- Male development not started
- XY
- External female development with no functioning internal reproductive organs
Y- Linked characteristics
- only present in males
- All male offspring exhibit the trait
- Y chromosome lost DNA over time
- Important for sex determination is SRY
What is dosage compensation?
the amount of protein produced by X-linked genes after randomly inactivated X- chromosomes
What is Random X - Chromosome inactivation?
One X chromosome turns to heterochromatin and turn off that X during development.
What are Barr bodies?
Hypercondensed X-Chromsomes
What does LncRNA do?
winds itself around X chromosomes to shut is down.
What would be required for a male calico cat?
XXY
How many Barr bodies do a male with XXXYY chromosomes have in each of his cells?
- 2 Barr bodies
What is complete dominance?
Phenotype of the heterozygote is the same as the phenotype of one of the homozygotes.
What is incomplete dominance?
Phenotype of the heterozygote is intermediate (falls within the range) between the phenotypes of the two homozygotes
What is Codominance?
Phenotype of the heterozygote includes the phenotypes of both homozygotes.
What is penetrance?
The percentage of individuals having a particular genotype that express the expected phenotype.
What is expressivity?
the degree to which a trait is expressed (ex; in polydactyly how many extra fingers)
What does a ratio of 2:1 mean?
one of the outcomes is lethal
Describe multiple alleles.
For a given locus, more than two alleles are present within a group of individuals
Describe gene interaction.
Effects of genes at one locus depend on the presence of genes at other loci.
Characteristics of gene interaction.
- genes exhibit independent assortment but do not act independently in their phenotypic expression
- The products of genes at different loci that interact to produce new phenotypes
What is epistasis?
One gene masks the effect of another gene.
A number of all white cats are crossed and they produce the following types of progeny; 12/16 white, 3/16 black, and 1/16 gray. What is the genotype of the black progeny?
A_bb or aaB_
What causes this ratio 12:3:1?
dominant epistasis (ex: color in squash)
What causes 9:3:4 ratio?
Recessive epistasis (ex: color in labradors)
What are the characteristics of cytoplasmically inherited traits?
- present in males and females
- usually inherited from the maternal parent
- reciprocal cross give different results
- exhibit extensive phenotypic variation, even within a single family
What is epigenetics?
phenomena due to alterations to DNA that do not include change in the base sequence; often affect the way in which the DNA sequences are expressed
What is genomic imprinting?
differential expression of genetic material depending on whether it is inherited from the male or female parent.
sex linked characteristics
genes located on the sex chromosome
sex influenced characteristics
autosomal genes that are more readily expressed in one sex
sex-limited characteristic
autosomal genes who expression is limited to one sex
genetic maternal effect
nuclear genotype of the maternal parent
cytoplasmic inheritance
cytoplasm genes, which are usually inherited from only one parent
genomic imprinting
Genes whose expression is affected by the sex of the transmitting parent
Discontinuous characteristics
relatively few phenotypes
continuous characteristics
continuous distribution of phenotypes; occurs when genes at many loci interact
polygenic characteristics
characteristics encoded by genes at many loci
pleiotropy
one gene affects multiple characteristics
What causes a 1:2:1 ratio?
incomplete or codominance
What causes a 9:3:4 ratio?
epistasis (weird ratios that equal 16)
Describe epistasis.
two genes working in a biochemical pathway together
What is required for typical male development?
- Y chromosome
- SRY gene
- MIH
- Testosterone
- Duct system
Explain complete dominance using dosage.
Complete dominance occurs because on dose of the proteins of the heterozygous genotype is the same phenotype as the homozygous genotype.
Explain incomplete dominance using dosage.
Incomplete dominance occurs because one dose of the heterozygous genotype doesn’t result in the same phenotype as the homozygous dominant due do a lack of protein dosage and leads to an intermediate phenotype.
Explain codominance using dosage.
codominance occurs when one dose of each two different alleles is expressed and produces a new phenotype.
How can we determine if a gene is incomplete or codominant?
biochemical process to determine which one/ can’t use genotype
