- Slides: 69
GENETICS THE FIELD OF BIOLOGY DEVOTED TO UNDERSTANDING HOW CHARACTERISTICS ARE PASSED FROM PARENT TO OFFSPRING.
GREGOR MENDEL (1823 – 1884) • AUSTRIAN MONK WHO STUDIED MATH & STATISTICS. • HE BECAME KNOWN AS THE “FATHER OF GENETICS”. • HE CONDUCTED EXPERIEMENTS ON PEA PLANTS.
MENDEL’S PEA PLANT EXPERIEMENTS • He observed 7 characteristics of pea plants – each characteristic had only 2 contrasting traits. - height flower position along the stem pod appearance pod color seed texture seed color flower color
MENDEL’S EXPERIMENT 1. GREW ONLY PLANTS THAT WERE PURE FOR EACH TRAIT. -he had plants self-pollinate for several generations. 2. CROSS-POLLINATED CONTRASTING TRAITS. -ex: he crossed a yellow pod plant with a green. 3. THE 1 ST CROSS WAS LABELED AS THE PARENTAL GENERATION (P).
4. THE OFFSPRING WERE LABELED AS THE F 1 GENERATION 5. MENDEL ALLOWED THE F 1 GENERATION TO SELF-POLLINATE & THOSE OFFSPRING WERE THE F 2 GENERATION.
MENDEL’S RESULTS • AFTER CROSSING A PURE GREEN PODDED PLANT (P) WITH A PURE YELLOW (P) ALL OF THE OFFSPRING WERE GREEN. • AFTER THESE OFFSPRING (F 1) WERE CROSSED THE RESULTING OFFSPRING (F 2) CAME OUT TO A 3 TO 1 RATIO FOR GREEN PODDED PLANTS.
MENDEL’S LAWS • LAW OF SEGREGATION -Reproductive cells only receive one factor of each pair. • LAW OF INDEPENDENT ASSORTMENT: -The factors for different characteristics are not connected
QUESTION EXPLAIN WHY MENDEL GOT THE RESULTS HE DID WITH THE PARENTAL GENERATION?
ANSWER Because the green color is considered dominant & it covers or masks the yellow color trait.
QUESTION If all of the offspring were green and then they were cross pollinated, why didn’t these offspring come out all green?
ANSWER Because the offspring from F 1 generation carried a hidden yellow factor that could be passed on to the offspring of F 2 generation.
GENETIC TERMS • Gene: a sequence of DNA that encodes for a certain trait • Allele: one of two (or more) alternative forms of a gene (a single letter) • Dominant Allele: an allele that dictates the expression of a trait (capital letter, ex: A) • Recessive Allele: an allele whose trait is masked by the presence of a dominant allele (lower case letter, ex: a)
TERMS • Genotype: genetic make-up of an organism (letter combination) • Phenotype: physical appearance of an organism (its outward appearance) • Homozygous: both alleles in a gene pair code for the same trait (ex: AA or aa) • Heterozygous: the two alleles in a gene pair that do not code for the same trait (ex: Aa)
TERMS • Sex Chromosome: the chromosome that determines the sex of an organism (the X and Y chromosome) • Autosome: any chromosome that is not a sex chromosome • Punnett Square: a chart which shows all possible gene combinations in a cross of parents • Monohybrid cross: a cross between two individuals for one trait (ex: Aa x Aa) • Dihybrid cross: crossing two different characteristics at the same time (Aa. Bb x Aa. Bb)
TERMS • Genotypic Ratio: the number of times each genotype appears in the offspring. Written from most dominant trait to the recessive. • Phenotypic Ratio: the number of times each phenotype appears in the offspring. Written from the dominant trait to the recessive. • Law of Segregation: factors that control a trait maintain a discrete identity when passed from parent to offspring.
Punnett Squares A Punnett square is a chart which shows all possible gene combinations in a cross of parents. – Horizontally across the top of the chart are the possible gametes of one parent. – Vertically down the side of the chart are the possible gametes of the other parent. – In the boxes of the chart are the possible T T genotypes of the offspring. TT x tt t t Tt Tt
B= brown eyes b= blue eyes GENOTYPIC RATIO: 1: 2: 1 BB: Bb: b b dominant: Homozygous Heterozygous: Homozygous recessive PHENOTYPIC RATIO: 3: 1 Brown: Blue Dominant: Recess ive Monohybrid Cross: two heterozygous individuals Bb x Bb B BB Bb bb
LET’S TRY ANOTHER ONE!!!! B= brown eyes b= blue The eyesgenotypic ratio is: 0: 2: 2 Bb x bb B b b Bb bb The phenotypic ratio is: 2: 2 1: 1
HOW DID MENDEL FIGURE OUT IF THE PURPLE FLOWERING PLANTS WERE HOMOZYGOUS DOMINANT OR HETEROZYGOUS?
The Testcross • A genetic procedure devised by Mendel to determine an individual’s actual genetic composition • A purple-flowered plant can be homozygous dominant (PP) or heterozygous (Pp) – One cannot tell by simply looking at the phenotype – One can tell from the results of a cross between the test plant and a homozygous recessive plant
How Mendel used the testcross to detect heterozygotes.
Pp. Qq x Pp. Qq Crossing 2 different characteristi cs at the same time.
P generation Analysis of a dihybrid cross Round, yellow Wrinkled, green
Rr. Yy x Rr. Yy Phenotypic Ratio
Dihybrid Cross EH EH EH Ee. HH & Ee. Hh H Eh EEH E= Brown h e= Blue eyes e. H Ee. H eyes H H= Brown hair h= Blond hair eh Ee. H h EEH H EEH h Ee. H H Ee. H h Cross e. H Ee. H H H Ee. H h h ee. H H H ee. Hh
AND THE Needs an E and H PHENOTYPIC Needs an E and 0/16 RATIO IS…. hh What does an offspring need to have brown eyes and brown hair? What is the chance of having that? 12/16 What does an offspring need to have brown eyes and blond hair? What is the chance of having that? What does an offspring need to have blue eyes and brown hair? What is the chance. Needs of having that? an ee 4/16 and H What does an offspring need to have blue eyes and blond hair? What is the chance of having that? 12: 0: 4: 0 Needs an ee and 0/1
How Genes Influence Traits • Genes specify the amino acid sequence of proteins – The amino acid sequence determines the shape and activity of proteins • Proteins determine a majority of what the body looks like and how it functions • Mutations in a gene result in new alleles – This ultimately leads to a change in the amino acid sequence and, hence, activity of the protein • Natural selection may favor one allele over another
Fig. 8. 11 The journey from DNA to phenotype
Fig. 8. 11 The journey from DNA to phenotype
Why Some Traits Don’t Show Mendelian Inheritance • Mendelian segregation of alleles can be disguised by a variety of factors – Complete dominance – Incomplete dominance – Codominance – Sex-linked – Environmental effects – Continuous variation – Epistasis
DIFFERENT TYPES OF DOMINANCE • COMPLETE DOMINANCE- a heterozygous & a homozygous dominant organism are the same phenotypically. –i. e BB=Bb
COMPLETE DOMINANCE B=brown eyes b=blue eyes All offspring will be…? Bb BB x bb B B b Bb Bb
• INCOMPLETE DOMINANCE- 2 or more alleles influence the phenotype resulting in a phenotype intermediate of the dominant and the recessive trait. + =
INCOMPLETE DOMINANCE FB= blue fur FR= red fur FB FB F BF B FR F BF R B B F F x B R F F WHAT ARE THE POTENTIALOFFSPRING’S PHENOTYPES? ? BLUE FURRED PURPLE FURRED
• CODOMINANCE- neither of the 2 alleles of the same gene totally masks the other. The result is a combination of both dominant traits.
CODOMINANCE R = red colored coat W= white colored coat R R W RW RW RR x WW All offspring will be …. . ? RED & WHITE !!
Blood Types • There are 6 genotypes. • They make up 4 phenotypes (blood types). • A and B are codominant, and O is recessive. Genotype Phenotype (Blood Type) IAIA or AA A IAi or AO A IBIB or BB B IBi or BO B IAIB or AB AB ii or OO O
What are the possible blood types of the potential children of an AB (IAIB) male and an B (IB i) female? What % chance will the offspring be type B? Hint: use a punnett square
IAIB x IBi IB i IA IB IAIB I BI B IAi I Bi What are the possible blood types of the potential children of an AB (IAIB) male and an B (IB i) female? TYPES: A, B, or AB What % chance will the offspring be type B? 50%
SEX LINKED TRAITS • THESE ARE TRAITS LOCATED ON THE SEX CHROMOSOMES. • MALES PASS GENES LOCATED ON THE “X” CHROMOSOME TO ALL OF THEIR DAUGHTERS & NONE OF THEIR SONS. • WHATEVER MOM HAS ON HER “X” CHROMOSOME WILL BE EXPRESSED IN HER SONS EVEN IF THE TRAIT IS RECESSIVE.
SEX LINKED ( X-LINKED) H= non hemophilia Xh. Xh x XHY h= hemophilia XH Y Xh Xh X HX h X h. Y WHAT ARE THE CHANCES OF HAVING A MALE WITH HEMOPHILIA? 100%
SEX INFLUENCED TRAITS • THE PRESENCE OF MALE OR FEMALE HORMONES INFLUENCES THE EXPRESSION OF CERTAIN TRAITS. – EX: PATTERN BALDNESS • IF FEMALE IS HETEROZYGOUS SHE WILL NOT BE BALD. -the gene is recessive in females • IF A MALE IS HETEROZYGOUS HE WILL BE BALD. -the gene is dominant in males
ENVIRONMENTAL EFFECTS • Many alleles are expressed depending on the environment. –Some are heat sensitive • Ex: Arctic foxes make fur pigment only when the weather is warm.
CAN YOU SEE WHY THIS TRAIT WOULD BE AN ADVANTAGE?
Continuous Variation • Most traits are polygenic – They result from the action of more than one gene • These genes contribute in a cumulative way to the phenotype – The result is a gradation in phenotypes or continuous variation Extremes are much rarer than the intermediate values
EPISTASIS • INTERACTION BETWEEN THE PRODUCTS OF TWO GENES IN WHICH ONE OF THE GENES MODIFIES THE PHENOTYPIC EXPRESSION PRODUCED BY THE OTHER. – EX: COAT COLOR FOR LABRADOR RETRIEVERS.
• The E gene determines if dark pigment will be deposited in the fur or not. • If the dog has ee there is no pigment & dog will be yellow. • The B gene determines how dark the pigment will be. • In yellow labs the B gene indicates the color on their nose, lips, & eye rims.
E_B_=black E_bb=chocolate/br own
B gene=black ee. B_ b= brown eebb
AUTOSOMAL TRAITS LOCATED ON ALL OF YOUR AUTOSOME CHROMOSOMES. YOU HAVE AUTOSOMAL RECESSIVE & AUTOSOMAL DOMINANT TRAITS.
SOME GENETIC DISORDER AUTOSOMAL RECESSIVE: ALBINISM CYSTIC FIBROSIS WILSON’S DISEASE TAY-SACHS DISEASE AUTOSOMAL DOMINANT HUNTINGTON’S DISEASE POLYDACTYLY PROGERIA DEAFNESS X-LINKED: HEMOPHILLIA COLORBLINDNESS
Epidermolysis Bullosa (EB) is a rare genetic disorder characterized by infection and blistering of the skin due to minor trauma. Almost 100, 000 Americans are infected by EB, the majority of which are children. Simple occurrences such as bathing, bumping into something, or even simple human touch can create new blisters or increase infection. While all forms of EB are painful some cases go as far as causing fusion of the fingers and toes, deformities, or in some cases even death.
Nail Patella Syndrome is a rare genetic disorder involving nail and skeletal deformities (among a host of other related anomalies) that occurs in approximately 2. 2 out of every 100, 000 people. It is transmitted as a simple autosomal dominant characteristic in the ABO blood group (Autosomal dominant means that you only have to inherit one copy of the gene to get it). It also means that there is no such thing as an unaffected carrier, and NPS CAN NOT skip a generation.
TRISOMY 13 – PATAU’S SYNDROME
Porphyria SENSITIVITY TO LIGHT –causes blisters, scarring, changes in pigmentation of skin, & increased hair growth
Sirenomelia: Mermaid syndrome
We all inherit a set of three Rhesus (Rh) genes from each parent called a haplotype. They are referred to as the c, d, e, C, D and E genes. The upper case letters denote Rh positive genes and the lower case, negative and we inherit either a positive or negative of each gene from each parent (eg. CDe/cde, cd. E/c. De etc. ). This means that we then possess two of each gene and can pass either to our offspring. If a person is tested Rh positive, their blood is said to contain the Rhesus factor - if they are tested negative it does not. A person possessing one or more positive Rh genes (C, D or E), anywhere in their inherited haplotypes, has inherited the Rh factor (eg. cd. E/De, cde/c. De etc. ) and they are tested Rh positive - only a person with a genotype of cde/cde is truly Rh negative.
The baby of an Rh negative woman may inherit the Rh positive factor from his/her father. This would result in the mother and baby having different blood types. During pregnancy, some of the baby's Rh positive red blood cells may enter the mother's circulation. The cells are recognized as being "foreign" by the mother's immune system, and she may produce antibodies. These antibodies can be permanent, and are capable of crossing over into the baby's blood and break down his/her Rh positive red blood cells; they will not harm the mother. Antibodies are usually produced too late in the first pregnancy to affect the baby being carried. Future babies are at risk since the antibodies are already present when pregnancy occurs.