Genetics What DNA is telling us!
Unit goals The student will investigate and understand common mechanisms of inheritance and protein synthesis. Key concepts include: a) understand the process of sexual reproduction, meiosis b) prediction of inheritance of traits based on the Mendelian laws of heredity c) genetic variation (mutation, recombination, deletions, additions to DNA); d) use of genetic information; and e) exploration of the impact of DNA technologies.
Let’s Go Back to Review Mitosis Mitosis= asexual reproduction in eukaryotic cells One division (PMAT) results in 2 identical diploid (2n) daughter cells Diploid (2n) means that chromosomes are paired, (remember one set comes from each parent) and this describes all body (or somatic) cells n=# of different chromosomes
Mitosis vs. Meiosis Meiosis= sexual reproduction in eukaryotic cells Two divisions (PMAT 1 and PMAT 2) results in 4 non-identical haploid (1n) daughter cells Haploid means that chromosomes are UNPAIRED and this describes ONLY reproductive cells (or sex cells or gametes or sperm & eggs) NOW Answer # 1-7
Mitosis vs. Meiosis # 8 • Start out special diploid germ cell • Two PMATs or divisions • Crossing over occurs & tetrad forms in Prophase 1 • 4 non-identical daughter cells • Haploid cells produced • Start out (usually) with same type of cell you begin with • One PMAT or division • NO crossing over or tetrad forms in Prophase • 2 identical daughter cells • Diploid cells produced
Mitosis vs. Meiosis # 9 • Start out with diploid cell (germ cell) • Uses PMAT (well, ok it does it twice) • Process produces daughter cells • Uses cell energy • Start out with diploid cell (parent cell) • Uses PMAT (nuclear division) • Process produces daughter cells • Uses cell energy
Meiosis- The Cold Hard Facts #10 & 11 • Starts with special diploid (2n, paired chromosomes) germ cell -46 chromosomes in humans • The FOUR daughter cells produced are either sperm or eggs and are haploid (1n, unpaired chromosomes) with genetically unique sets of chromosomes due to crossing over
Why Bother with Sexual Reproduction? #12 • mitosis • Genetically identical “clone” no variety • Changing environment can lead to extinction • Genetic variations only through mutation • All of genes good or bad are passed on so it is difficult to rid the population of a bad gene • meiosis • Increased genetic diversity and variety • New genetic variations may have adaptations that help survival of the organism • Since only ½ of each parent’s genes are passes to the offspring, bad genes passed on can be eliminated from population more easily
Why Bother with Sexual Reproduction? #12 & 13 • meiosis • Slower and more energy demanding • More complex process with more possible chances for chromosomal errors • mitosis • More rapid and uses less energy • In stable environment, resulting organism will be successful
Sperm & Egg Formation • Sperm formation produces 4 nonidentical haploid sperm cells • Egg formation produces one haploid egg (ovum) cell and 3 polar bodies (which are resorbed and do not become eggs)
Nondisjunction • Nondisjunction is an error during anaphase (of mitosis or anaphase 1 or 2 of meiosis) resulting in the WRONG number of chromosomes in the resulting cells • Effects the offspring if it occurs during meiosis BECAUSE then the resulting offspring will have the WRONG number of chromosomes
Steps of Meiosis -PMAT 1 & 2 • Interphase 2 • Short • No DNA replication • Prophase 2 • Metaphase 2 • Anaphase 2 • Sister chromatids separate • Telephase 2 & cytokinesis • Interphase 1 • Prophase 1 • Tetrads form • Crossing over • Metaphase 1 • Anaphase 1 • Cells become haploid when tetrads separate • Telephase 1 & cytokinesis
Meiosis • Go to http://www.cellsalive.com/meiosis.htm and go through the steps of meiosis • Complete the chart in your packet using this animation on this site or your textbook
vocabulary terms INHERITANCE or HEREDITY- The genetic transmission of characteristics from parent to offspring, such as hair, eye, and skin color.
vocabulary terms HOMOLOGOUS CHROMOSOME-A pair of matching chromosomes in an organism, with one being inherited from each parent.
vocabulary terms AUTOSOME- A chromosome that is not a sex chromosome.
vocabulary terms GENOTYPE- the genes present in the DNA of an organism. There are always 2 letters in the genotype because (as a result of sexual reproduction) 1 gene from MOM + 1 gene from DAD = 2 genes (2 letters) foroffspring
vocabulary terms Now, it turns out there are 3 possible GENOTYPES: 1. 2 capital letters (like "TT") 2. 1 of each ("Tt") 3. 2 lowercase letters ("tt"). Since WE LOVE VOCABULARY, each possible combo has a term for it.
vocabulary terms • HOMOZYGOUS: GENOTYPE has 2 capital or 2 lowercase letters (ex: TT or tt) ("homo" means "the same") • Sometimes the term "PUREBRED" is used instead of homozygous.
vocabulary terms • HETEROZYGOUS:GENOTYPE has 1 capital letter & 1 lowercase letter (ex: Tt) ("hetero" means "other") • A heterozygous genotype can also be referred to as HYBRID and sometimes the organism is called a CARRIER
vocabulary terms Let's Summarize: Genotype- genes present in an organism (usually abbreviated as 2 letters) • TT = homozygous = purebred • Tt = heterozygous = hybrid • tt = homozygous = purebred
vocabulary terms • PHENOTYPE- how the trait physically shows-up in the organism; it is the observable traits present in an organism What the organism LOOKS like • Examples of phenotypes: blue eyes, brown fur, striped fruit, yellow flowers
vocabulary terms • POLYGENIC INHERITANCE- a trait controlled by two or more genes that may be on the same or on different chromosomes • Examples of polygenic inheritance: eye color, skin color, and height
vocabulary terms • ALLELES- alternative forms of the same gene. Alleles for a trait are located at corresponding positions on homologous chromosomes called loci. ALLELES Chromosome from MOM A b C d e Chromosome from DAD A B c d E
(P) Chromosome from DAD: P Chromosome from MOM: p (p)
vocabulary terms • When 1 allele masks (hides) the effect of another, that allele is called DOMINANT and the hidden allele is called RECESSIVE.
vocabulary terms • Dominant alleles are represented by a CAPITAL letter • Recessive alleles are represented by a LOWERCASE letter
What are Dominant Genes? • Dominant Genes = one gene overshadows the other • Angus Cattle: black is dominant, red is not Dominant: BB or Bb Recessive: bb ONLY
What are Dominant Genes? Hereford: white face is dominant Dominant: WW or Ww Recessive: ww ONLY
What are Dominant Genes? • Hampshire Hog: white belt is dominant Dominant: WW or Ww Recessive: ww ONLY
What are Recessive Genes? • The gene that is overshadowed by a dominant gene • Recessive genes can only express themselves if BOTH genes are recessive
What are Recessive Genes? • Horned is recessive to polled. Dominant: PP or Pp Recessive: pp ONLY
What are Recessive Genes? Black wool is recessive to white wool. Dominant: WW or Ww Recessive: ww ONLY
What are Recessive Genes? • Some types of dwarfism are recessive to average size. Dominant: DD or Dd Recessive: dd ONLY
What are Recessive Genes? • Albinism (Albino) is recessive to pigmented.
What makes an organism the way that it is? • NATURE vs. NURTURE · Traits that are expressed through genes can be inherited. Characteristics that are acquired through environmental influences, such as injuries or practiced skills, cannot be inherited.
Gregor Mendel (1822-1884) • Austrian monk • Called the “Father of Genetics" for his study of the inheritance of 7 traits in pea plants.
Gregor Mendel (1822-1884) • The traits that Mendel chose to study were easily observable in 2 distinct forms. • EX.: Stem Height - tall vs. short • Pod Shape - round vs. wrinkled • Flower Color – white vs. purple • Seed Color – green vs. yellow
Gregor Mendel (1822-1884) • The significance of Mendel's work was not recognized until the turn of the 20th century • Its rediscovery prompted the foundation of genetics.
Geneticists apply mathematical principles of probability to Mendel’s laws of heredity in order to predict the results of simple genetic crosses
Mendel’s laws of heredity are based on his mathematical analysis of observations of patterns of the inheritance of traits. • The laws of probability govern simple genetic recombinations. • To see this we use a Punnett Square
Punnett Squares • To complete a Punnett square, we use a letter to represent each allele. • We represent the dominant allele with a capital letter, and the recessive allele is given the same letter but in lowercase.
Punnett Squares • For the pea plant flowers: dominant: purple color = P recessive: white color = p. • If both parents( P generation) are purebred, then the purple colored parent must be PP and the white colored parent must be pp.
How can we predict these results? Homozygous-dominant We complete the possible combinations. P P p P P p p p P P p p Homozygous-recessive
These results show that all the F1 (1st filial generation) offspring are all purple colored hybrids. 100% purple offspring