DNA Structure, Function, and Genetic Inheritance: Key Concepts for Biology

DNA

Entire genetic information about an organism

Chromosome

Tightly coiled linear piece of DNA

Gene

A specific section of DNA found on a chromosome

Allele

Alternate form or variation of a gene

Base Pair

Two complementary nucleotides

Nucleotides

Simple building unit of DNA

DeoxyriboNucleic Acid

DNA is a nucleic acid composed of nucleotides

Nucleotide parts

Sugar (deoxyribose), Phosphate group, Nitrogen Base (four total)

Purines

Two types of nitrogen bases: Adenine & Guanine

Pyrimidines

Two types of nitrogen bases: Cytosine & Thymine

Thymine

Only found in DNA

DNA strands

Run in opposite directions and are complementary not exact

Hydrogen bonds

Hold DNA strands together

Sugar/Phosphate

Make up the backbone of DNA strands

DNA location

DNA is in the nucleus of animal cells

Double helix

DNA appears as a spiral staircase in the cell

DNA function

Storage of information about an organism

DNA replication

DNA makes exact copies of itself before new cells are made

DNA mutation

Changes in the original line up of nucleotides

Transformation

Introduction of new DNA into a bacterial cell; called transfection in animal cells

Gametes

Sexually reproducing cells, including egg cells in females and sperm cells in males

Homologous chromosomes

Chromosomes that are the same length, shape and carry the same genes in the same order

Diploid

Have two copies of each chromosome (one from each parent)

Haploid

Having only one copy of each chromosome

Autosomes

Chromosomes that determine non-sex characteristics of an individual

Sex Chromosomes

Chromosomes that determine the sex of an individual (XX females, XY males)

Meiosis

Nuclear division that will NOT produce genetically identical cells

Crossing over

Exchange of genetic info between homologous chromosomes

Polyploid cell

Having one or more complete sets of extra chromosomes

Aneuploid cell

Having only a few extra or missing chromosomes because of non-disjunction

Non-disjunction

Failure of homologous chromosomes to separate during meiosis

Trisomy 21

Formed from non-disjunction in the autosomes

Down Syndrome

Results from Trisomy 21.

Trisomy 18

Having three copies of chromosome 18.

Edward's Syndrome

Results from Trisomy 18.

Turner's Syndrome

Formed from non-disjunction in the sex chromosomes; a female with only one copy of the X chromosome. Her genotype is (XO).

Symptoms of Turner's Syndrome

Females are sterile, small in stature, show signs of mental impairment, and lack or have diminished secondary sexual characteristics.

Trisomy X

Formed from non-disjunction in the sex chromosomes; a female with three copies of the X chromosome. Her genotype is (XXX).

Klinefelter Syndrome

Formed from non-disjunction in the sex chromosomes; a male with two copies of the X chromosome and one copy of the Y chromosome. His genotype is (XXY).

Symptoms of Klinefelter Syndrome

Males will be sterile and have mixed secondary sexual characteristics.

Jacob's Syndrome

Formed from non-disjunction in the sex chromosomes; a male with two copies of the Y chromosome and one copy of the X chromosome. His genotype is (XYY).

Symptoms of Jacob's Syndrome

Male is 'Normal'.

Punnett Square

Tool used by scientists to predict genotype and phenotype.

Dominant allele

Use an Uppercase letter.

Recessive allele

Use Lowercase letter.

Homozygous

Use the same letters; must have a last name; (Dominant/Recessive).

Heterozygous

Use different letters; (upper & lowercase letters).

Steps of a Punnett square

1. Assign letters to each characteristic; 2. Assign appropriate letters to each parent; 3. Draw a Punnett square; 4. Add letters to the Punnett square; 5. Predict genotype & phenotype.

Mendel's 5 Part Hypothesis

1. Every gene of DNA will have two alleles; 2. Law of Segregation: alleles will separate during meiosis; 3. Law of Independent Assortment: allele separation is completely random; 4. One allele is dominant and one allele is recessive; 5. Individuals are homozygous or heterozygous.

Multiple alleles

Many genes will have more than one allele because of mutations.

Co dominance

Two dominant alleles are being expressed equally.

Incomplete dominance

The dominant allele does not completely hide the recessive allele. A heterozygote is an intermediate of both alleles.

Polygenic inheritance

Many genes control one physical characteristic.

Pleiotropy

One gene controls many physical characteristics (the SRY gene in males).

Sex linked

Trait determined by a gene carried on the sex chromosomes.

Dosage compensation

Inactivation of one X chromosome in females (ensures equal protein production between males and females).

Barr Body

Highly condensed, inactivated X chromosome attached to the nuclear membrane.

Mosaics

Females that are heterozygous for X chromosomes will have random inactivation.