Unit 3 Module 2 — How Genetic Diseases Are Inherited Flashcards
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38 Terms
Q: About how many genes are in the human genome?
Humans have about 19,000 different genes in their genome.
Q: Define allele.
is a variation of a gene caused by small changes in the nucleotide sequence.
Q: How does DNA become a chromosome?
DNA wraps around proteins called histones to form nucleosomes, which coil and condense into chromosomes.
Define diploid.
(2n) cell has two copies of each chromosome—one from each parent.
Q: Define haploid.
(n) cell has only one set of chromosomes, such as an egg or sperm cell.
Q: How many chromosomes are in a human?
Humans have 46 chromosomes (23 pairs).
Q: Define homologous chromosomes.
are matching pairs—one from each parent—that carry the same types of genes.
Q: What are sister chromatids?
Identical copies of a chromosome connected by a centromere after DNA replication
Q: What does a dominant gene mean?
A dominant allele masks the effect of a recessive allele and determines the expressed trait.
Q: What does a recessive gene mean?
A recessive allele’s effect is hidden when a dominant allele is present; it’s expressed only when both alleles are recessive.
Q: How many copies of a dominant gene must be present to express a dominant trait?
Only one copy is needed.
Q: How many copies of a recessive gene must be present to express a recessive trait?
Two copies (homozygous recessive) are required.
Q: What does “carrier” mean?
has one normal and one recessive allele; they do not show symptoms but can pass the trait to offspring.
Q: What is a karyotype?
A picture or chart showing all of an individual’s chromosomes, used to detect abnormalities.
Q: What is an autosome?
Any chromosome that is not a sex chromosome (pairs 1–22).
Q: What are the sex chromosomes?
The 23rd pair—XX in females, XY in males.
Q: Define meiosis.
A type of cell division that reduces chromosome number by half and produces four haploid gametes.
Q: What is the result of meiosis?
Four genetically unique haploid cells (sperm or eggs).
Q: How many rounds of division are required in meiosis?
Two—Meiosis I and Meiosis II.
Q: What is crossing over and when does it occur?
The exchange of genetic material between homologous chromosomes during Prophase I, creating genetic variation.
Q: What is independent assortment and when does it occur?
The random distribution of maternal and paternal chromosomes during Metaphase I.
Q: What is a tetrad and does it form in Meiosis I or II?
A pair of homologous chromosomes (four chromatids total) that form during Prophase I of Meiosis I.
Q: What is the stage called between Meiosis I & Meiosis II?
Interkinesis
Q: Define spermatogenesis
meiosis in males, forming four sperm cells
Q: Restate Mendel’s law of segregation in your own words.
Each organism has two alleles for every trait, which separate during gamete formation so each gamete carries only one allele.
Q: In a pedigree, a square designates what?
A male
Q: In a pedigree, a circle designates what?
A female
Q: In a pedigree, a shaded square or circle designates what?
An affected individual (shows the trait)
Q: In a pedigree, a half-shaded square or circle designates what?
A carrier of the trait
Q: In a pedigree, a horizontal line designates what?
A union or marriage.
Q: In a pedigree, a vertical line designates what?
Offspring (children) from that union.
Q: Where are the generational numbers located on a pedigree?
On the left side, listed vertically (Generation I, II, III, etc.).
Q: What are the characteristics of an autosomal recessive pedigree?
Trait can skip generations.
Males and females equally affected.
Carriers may not show symptoms.
Q: What are the characteristics of an autosomal dominant pedigree?
Trait appears in every generation.
Only one copy of the dominant allele needed.
Affected individuals usually have an affected parent.
Q: Write a genotype for incomplete dominance and give a phenotypic example.
Genotype: Rr (heterozygous) → Phenotype: intermediate trait (e.g., pink flower from red × white parents).
Q: Write a genotype for multiple alleles and give a phenotypic example.
Genotype: I^AI^B → Phenotype: type AB blood.
Q: How many blood types are present in humans?
Four—A, B, AB, and O.
Define Oogenesis
meiosis in females, forming one egg cell.