Genetics & Chromosomes Flashcards

Genetics

Branch of biology that deals with heredity and the expression of inherited characteristics.

Heredity

Transmission of traits from one generation to another.

Traits

An expressed characteristic that can include the presence or absence of disease.

Chromosomes in Humans (w/ location)

23 chromosomes in the egg and 23 in sperm.

Fertilization

Two copies of each chromosome: 23 chromosomes received from one parents 23 from other parent.

Diploid Cell (2n)

Most cells of our body; containing 2 complete sets of chromosomes (1 each via parents); chromosomes found in pairs called homologous pairs

Genes

Segments of DNA that code for specific proteins.

Alleles

Different forms of a gene, two per gene. Produce various versions of the trait they determine.

Dominant

When effects of an allele can be detected regardless of another allele that may be present. Usually represented as an uppercase letter (like A).

Recessive

When the effects of an allele are masked by another allele when its present. Usually represented by a lowercase letter (like a).

Homozygous

Two copies of the same allele for a gene. (AA or aa).

Heterozygous

Two different alleles for the same gene. (Aa)

Genotype

Alleles that are present for a particular gene.

Phenotype

Observable physical traits of an individual.

Gamete Formation

1. 2 alleles for each gene found as homologous chromosomes that separate and move towards opposite ends of the cell during meiosis 1.

2. Meiosis 2: sister chromatids pulled apart resulting in 1 copy of each chromosome per gamete.

Punnett Square

Matrix that's used to predict genetic makeup of offspring of individuals of particular genotypes.

Pedigrees

Charts showing genetic/phenotypic connections among individuals in a family. Especially useful in following recessive genes through a human population.

Karyotype

Picture of chromosomes to check for genetic abnormalities

Deletion

Loss of a piece of/whole chromosome.

Duplication

Addition of piece of/whole chromosome.

Prenatal Genetic Testing

Recommended when:

• Defective gene runs in family

• Mother is older than 35, increased risk of chromosomal abnormalities

Amniocentesis

• Small amount of amniotic fluid withdrawn (contains cells of the fetus)

  • Usually performed 15-20 weeks after last menstrual period

• Cells grown and examined for abnormalities in number and structure of chromosomes.

Cronic Villi Sampling (CVS)

• Involves taking a small piece of chorionic villi (part of the placenta).

• Cells grown and examined for abnormalities in number and structure of chromosomes.

• Disadvantage of CVS is its slightly greater risk of triggering miscarriage than does amniocentesis.

Blood Draw from Mother

• DNA from fetus can be found in the mother’s blood

  • Blood sample can be screened for various genetic abnormalities

• Advantages: non-invasive for the fetus, so it doesn’t increase risk of miscarriage; can be done earlier in pregnancy

• Disadvantages: higher rate of false positives

  • Positive tests often need to be followed by additional tests.

Newborn and Adult Genetic Testing

• Many predictive genetic test are now available of being developed.

• Some tests identify people who are at risk or predisposed for a specific disease before symptoms appear.

Chromosomes

threadlike structures made of DNA and associated proteins (especially histones)

Somatic cells

all the cells of the body (soma), except for gametes 

human somatic cells have 46 chromosomes (23 pairs)